I live in Hemel Hempstead and am trying to find somewhere that is no more than about 1 1/2 hours away
I've been to rye meads, rainham marshes, College lake and Tring reservoirs and amwell and it doesn't have to necessarily be rspb
Do not know your area Benji but googled and have attached the snapshot, other places as well.
I am not familiar with your area but it is worth remembering that wildlife does not confine itself to reserves run by big agencies such as RSPB or WWT. Local wildlife trusts have smaller reserves that will probably be closer to you and in most cases entry is free,It will probably worth Googling your local wildlife trust.
All good suggestions and all I would offer as well.
Google Maps is probably one of the best places start, just by putting in something random like wildlife reserves, and fine tuning it to RSPB or Wildlife Trust.
Another big and very likely possibility, is National Trust, a lot of properties will have substantial grounds or parklands, with the added plus, the National Trust will do what it can to support wildlife. I have a couple of very good Nat Trusts which offer some fabulous wildlife and plantlife opportunities.
Add to that, many birds do frequent buildings, and though many swifts and swallows will have started their flights south, house martins will still be very active on many old Nat Trust buildings.
Within half an hours drive from me, there is a rather large fishing lake, and that also makes for good wildlife viewing. The only other folk there are just the anglers, and many of them while sitting along the lakeside, will have a good knowledge of wildlife and will often give the time of day for a quiet relaxed chat. That is until they see the float bob up and down and need to reel the fish in. But they will often apologise and continue the chat.
Though I don't frequent English Heritage sites, and I have no idea why not, so I need to remedy that, but they too will have lots of wildlife.