London has a lot of good coin dealers.
If you wish to compare your coins with known genuine ones, London is one of the best cities in the World to locate a coin dealer to find comparison coins.
Try a 'phone ring around explaining your your coins and and take them to a dealer you have chosen. Scan a commercial telephone book for advertisments of coin dealers, to choose which dealers you ring. A comprehensive commercial telephone book for London can be located in Post offices.
If I were to visit London again, I would perhaps do a 'Pub Crawl' with my friends, but I would do a 'Coin Dealer Crawl' by myself over a couple of days, just for my own numismatic entertainment!