I'm Surrey based so can't say I've been to Mere Sands. Sorry. Your latest pic is also of a Reed Bunting. What's happening is that the head and throat feathers were moulted at the end of last year's breeding season (by which time an adult bird's feathers are pretty worn and knackered) and the tips of these 'new' feathers are now being actively abraded to slowly reveal the breeding plumage. In the male Reed Bunting this consists of a black head and breast patch with obvious pale 'moustache'. Give it a few more weeks and the tips will be fully abraded revealing a stunning bird in full breeding livery. Shame the song doesn't quite live up to the plumage!

To be fair, Reed Buntings and male House Sparrows are pretty similar so it's easy to confuse the two. Check the crown and habitat preferences though. Then have a look at Marsh and Willow Tits or Willow Warblers and Chiffchaffs...and if you're still keen after that you've definitely got the birding bug

All the best,
Gibster.