The National Archives has several hundred German Capture cards available online for PoWs captured in the Cassel area, these for Cassel itself, for example. I have found over 800 so far but place names can have various spellings, e.g. three for Watou and four in the case of Cassel. The vast majority are in the first half of the alphabet by family name, which perhaps explains why I can't find Harry i.e. they are still working through putting them online (some time later there are no additional entries). I was hoping to find his record as amongst other things they give which camp each PoW was sent to.

A lot of the records seem to be missing as those for neither John Wests's father nor Harry have come to light. By searching the database for the short span of dates when Cassel and area were overrun and places of capture I came up with 14 spelling variations for Wormhout, 22 for Watou, 22 for Cassel, and no less than 54 for Hazebrouck! Subsequently I searched on Regiment for '53', '53rd' and the individual battery numbers. Still no Harry but I did find records for at least 14 (possibly 15) members of 53rd RA (reproduced here as they appear in the database with the exception of the family name before the given name(s)):

	DOB	Place of Birth	Regiment/Unit	Army No.	Date captured	Place captured	Camp	PoW No.
Allaway, Douglas	4 December 1918	[unspecified]	53 Anti-Tank Regiment, 209 Battery	1524793	29 May 1940	Cassel, France	Stalag XXA Thorn Podgorz	25979
Davies, George [Henry]	15/08/1919	Beiles Corner, Bewdley	[211/53 Anti Tank Regiment], Royal Artillery	1471073	[unspecified]	[unspecified]	[unspecified]	[unspecified]
Evans, William George	21/7/1918	Aberdare, South Wales	(53 Regiment?) Royal Artillery	1491358	30 May 1940	Walou	Stalag XXA Thorn	13772
Fletcher, [Leonard]	Age: [20]	unknown	[210 Battery, Anti Tank Regiment, Royal Artillery]	1435239 [1465269]	[unspecified]	[unspecified]	[unspecified]	[unspecified]
Graham, Henry	2 February 1905	Newburne	53 Anti-Tank Regiment, 210 Battery, Royal Artillery	1055456	28 May 1940	Bethaume	Stalag VIIIB Lamsdorf	14449
Holland, William	3 August 1918	London	53 Anti Tank Regiment, 211 Battery	1491400	29 May 1940	Cassel	Stalag XXA Thorn	11465
Jordan, George Arthur	26/10/13	St Marys, Kidderminster	53rd Regiment, Royal Artillery, 211 Company	5248931	28/05/40	Cassel	Stalag VIIIB Lamsdorf	15729
Lewin, John Edward	04/08/1906	Newcastle	210 Battery 53rd Regiment Royal Artillery	1062106	28 May 1940	Dunkirk	Stalag VIA Hemer	26459
Lovett, George	05 August 1903	Wolverhampton	209 Battery Anti-Tank Regiment, Royal Artillery	1057352	[unspecified]	[unspecified]	Stalag XXA Thorn	20460
Mills, Leonard Lawrence	13/01/14	Kiddiminster	53 Anti-Tank Regiment, Royal Artillery, 209 Battery	829873	29/05/40	[unspecified]	Stalag XXA Thorn	11172
Nicholls, Frank George	19/05/19	Kidderminster	53rd Anti-Tank Regiment, Royal Artillery	1440023	30/05/40	Watou	Stalag VIIIB Lamsdorf	10677
Shackleton, Jonas	19/11/18	Halifax, Yorkshire	53 Anti-Tank Regiment , Royal Artillery	1514931	28/05/40	Watou	Stalag VlllB Lamsdorf	10072
Skelding, Syd Howard	20/11/14	Cradley Heath	53rd Regiment, Royal Artillery	877216	30/05/40	Watou	Stalag XXA Thorn	11392
Sleck, Arthur Townsend George	13/04/16	Tredegar, Monmouthshire	53rd Anti-Tank regiment, Royal Artillery	1439482	29/05/40	Cassel	Stalag VIIIB Lamsdorf	9857
Sutton, Victor	17/11/19	Stourport	Royal Artilley	859903	29/05/40	Cassel	Stalag XXA Thorn	13760

With three batteries 209, 210 and 211 being in the Cassel area (212 was further north in Bergues) each consisting of three troops of four men there would have been 36 gunners and perhaps a driver and sergeant for each troop making 55 men altogether, very few if any returning to England without being captured. Harry mentions 19 men by name of whom two were injured and evacuated prior to Cassel and four died in various actions, leaving up to 13 almost certainly captured but only Vic Sutton can be found for certain in the National Archives and one possible (Davies). John Lewin of 210 Battery is recorded as having been captured at Dunkirk, the date given is 28th May which may raise a question-mark over the place, but his camp is give as Stalag 6A which is in Hemer, Dortmund in western Germany and a very long way from the Polish camps where all the others were sent so he may have opted to go it alone and nearly made it.

August 2025: Additional records have come to light on WW2Talk.com. I found Gnr Crumpton in the 'big list' of more than 800 people captured in the area or at that time but it had no information on Regiment let alone Battery which is why I didn't include it in the above table (there may be others). Sadly although Gnr Crumpton survived the fighting and capture he died in POW camp:

	DOB	Place of Birth	Regiment/Unit	Army No.	Date captured	Place captured	Camp	PoW No.
Crumpton, Lewis	3 November 1921	Kidderminster	53 Anti-Tank Regiment, 211 Battery	1459434	30 May 1940	Cassel, France	Stalag XXA Thorn	13756

That led to a further list posted by Kyle on the same thread taken from the Army Roll of Honour 1939-1945 of those who died before capture:

	YOB	Place of Birth	Date of Death	Rank	Regiment/Unit
HUTTON-SQUIRE, ROBERT DAVID	1909	Yorkshire.	30 May 1940	Second Lieutenant	53 (The Worcestershire Yeomanry) Anti-Tank Regiment
BOWNS, HORACE JAMES	1919	Monmouthshire.	28 May 1940 - 30 May 1940	Gunner	210 Battery, 53 (The Worcestershire Yeomanry) Anti-Tank Regiment
FLETCHER, LEONARD	1920	Birmingham.	28 May 1940 - 2 Jun 1940	Gunner	210 Battery, 53 (The Worcestershire Yeomanry) Anti Tank Regiment
GRINDROD, WILLIAM ANSON GOODWIN	1919	Salford.	28 May 1940 - 30 May 1940	Gunner	210 Battery, 53 (The Worcestershire Yeomanry) Anti-Tank Regiment
EDWARDS, GEORGE VERDUN	1916	Worcestershire.	25 Nov 1940	Serjeant	53 (The Worcestershire Yeomanry) Anti-Tank Regt.
CARTLAND, JOHN RONALD HAMILTON	1907	Worcestershire.	30 May 1940	Major, Acting Lieutenant Colonel	53 (The Worcestershire Yeomanry) Anti-Tank Regt.
GARDNER, JOHN AUSTIN	1920	Worcestershire.	28 May 1940	Bombardier	211 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regt.
TANNER, HUBERT	1921	Walsall.	16 May 1940	Gunner	209 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regt.
SLY, RONALD CHARLES	1920	Worcestershire.	28 May 1940	Gunner	211 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regt.
WHITEHOUSE, CHARLES ARTHUR	1919	Worcestershire.	10 May 1940	Gunner	211 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regt.
BUTCHER, RONALD	1920	Worcestershire.	28 May 1940	Gunner	211 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regt.
EAMES, SIDNEY TREVOR	1918	Worcestershire.	28 May 1940	Bombardier	211 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regt.
HILTON, JOHN ALFRED HAROLD	1905	Birmingham.	17 May 1940	Bombardier	53 (The Worcestershire Yeomanry) Anti-Tank Regt.
KOPPEL, LOUIS		Dundee.	12 May 1940	Gunner	53 (The Worcestershire Yeomanry) Anti-Tank Regt.
HARMER, FREDERICK JOHN	1918	Hereford.	28 May 1940	Gunner	211 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regt.
GINNS, FRANK DOUGLAS	1919		28 May 1940	Gunner	211 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regt.
BOLTON, BENJAMIN CHARLES	1911	Hull.	28 May 1940	Gunner	209 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regt.
GRINDROD, WILLIAM ANSON GOODWIN	1919	Salford.	28 May 1940 - 30 May 1940	Gunner	210 Battery, 53 (The Worcestershire Yeomanry) Anti-Tank Regiment
BOURNE, HAROLD WILLIAM	1909	Sussex.	28 May 1940	Gunner	211 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regt.
BOTFIELD, THOMAS HENRY	1918	West Bromwich.	29 May 1940	Gunner	211 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regt.
HESFORD, ROSS		Middlesex.	16 May 1940	Serjeant	209 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regt.
BARNES, THOMAS WILLIAM	1918	South East London	10 May 1940	Gunner	211 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regt.
EDKINS, JOHN SAMUEL	1920	Birmingham.	28 May 1940	Bombardier	210 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regt.
KNIGHT, ROLAND THOMAS	1913	Birmingham.	16 May 1940	Bombardier	210 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regt.
FLINT, JOSEPH	1914	Sheffield.	29 May 1940	Gunner	209 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regt.
OSBORNE, FREDERICK	1904		18 May 1940	Gunner	53 (The Worcestershire Yeomanry) Anti-Tank Regiment
REDDELL, WILLIAM GEORGE	1920		27 May 1940	Gunner	210 Battery, 53 (The Worcestershire Yeomanry) Anti-Tank Regiment
FLETCHER, LEONARD	1920	Birmingham.	28 May 1940 - 2 Jun 1940	Gunner	210 Battery, 53 (The Worcestershire Yeomanry) Anti Tank Regiment
WRIGHT, ERIC	1918		28 May 1940 - 2 Jun 1940	Gunner	210 Battery, 53 (The Worcestershire Yeomanry) Anti-Tank

With these additional ones found on the CWGC database:

	YOB	Date of Death	Rank	Regiment/Unit
PLEVEY, PHILIP	1921	17 May 1940	Gunner	209 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regiment
BRADLEY, GEORGE WILLIAM	1916	16 May 1940	Gunner	209 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regiment
MICKLEWRIGHT, VICTOR LESLIE		28 May 1940	Gunner	211 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regiment
COX, BERNARD ROY	1916	26-29 May 1940	Gunner	211 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regiment
OLIVER, ERNEST		28 May 1940	Gunner	211 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regiment
PRITCHARD, GEORGE DOUGLAS	1919	28 May 1940	Gunner	211 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regiment
REILLY, AUSTIN	1919	28 May 1940	Gunner	211 Bty., 53 (The Worcestershire Yeomanry) Anti-Tank Regiment

This gives a further 31 Other Ranks in Batteries 209, 210 and 211 (plus 2 unknown) making 50 in total so much closer to the estimated number, but still leaves around 10 that Harry mentions by name unaccounted for.