Locative names of regiments did not really mean anything until 1873 when permanent depots were establishment for the line regiments. A particular Colonel may decide to have a recruiting party in their named county, but most recruits were picked up as they moved around the UK. When the service companies were overseas they left a depot company at home to carry on finding and training recruits. For the 48th they had a second battalion from 1804 to 1814.
Findmypast are supposed to have all pension records but he is not there. I also checked the old National Archives index for men discharged to pension before 1854 which should match with FindMyPast but again no luck. Normally men enlisted for unlimited service, ie for life. In reality they were given a medical after 21 years and most were discharged to pension. They could be discharged to pension sooner for medical reasons or when there was a reduction in the armys strength.
During the wars with France and the USA they introduced seven year limited service, but without a pension
I have a muster for the 48th Foot from 1816 and he is not listed. Both battalions served in Spain, with the 2nd Bn returning home in 1811. Looking at the clasps - Talavera (1809), Busaso (1810), Albuhera (1811), Badajoz (1811), Vittoria (1813), Pyrennes (18), Toulouse (1814) so he must have been in the 1st Bn for the last three.
One potential problem is that the 48th do not have Busaco as a battle honour. So either he invented it the medal was not issued until 1848/49 or he was part of a small contingent of 48th men; or he transferred to another regiment. In order to research him further you will have to go to Kew and look at the muster books, possibly for both battalions. He almost certainly started with the 2nd Bn, but I would start with the 1st Battalion in 1814. By going forward until he is discharged you may get an explanation about his pension. If you have the time you can go backwards from 1814 until he enlists. But each battalion will have separate muster books. So you will have to search both if he transfers.
Ken