Military Date: 7 Apr 1809". This is not shown on the original record so where might Ancestry have got that date from and what does it mean?
These images are scans of open ledgers with the record continuing on the opposite page. Have you looked at the next image?
ShaunJ you are a star! I had simply viewed the image presented to me but having taken your advice I see there is indeed a second page with a lot more information. Firstly is states that it is a record for the 1st battalion of the 82nd Foot, not the 2nd as was suggested earlier. Against my "ancestor" under Attestation is that mysterious date 7 Apr 1809, which is presumably the date he signed up. That second page also shows that he died on 25 Oct 1812 (Napoleonic Wars?) which means that he is not after all my 3G Grandfather as my 2G Grandfather was born in 1819! However, this hasn't been a wasted exercise as he might still be a relative and I have learned quite a bit about military history and military records, so many thanks to everyone who has responded.