Mmm......The bullhead in the lower Thames, well they are obviously there but I wouldn't say in abundance and it's a big river
good luck though mate and certainly worth the challenge, I'd seriously do some research for the bullhead on small rivers aswell as I feel you may find the overall fishing just a little easier for em,
Incidentally have you had any bullhead from the lower Thames previously
Personally I'd use a whip with flick tip or a small net
Don't exactly know how you'll fair with the 3 spined stickle back though as I'd say these are becoming rather rare over the years,
I can well remember catching these meself as a kid on light tackle in me local park pond but sadly I've not seen these now for some 33 years
Might be well worth adding the gudgeon to yer list aswell, loverly pretty little fish these
Stone loach are now rare but can be found in small chalk streams and best targeted at night and with a net and head lamp as these are very much nocturnal, incidentally you'll probably find bullhead in these type of streams aswell