Yeh im from london.
YES try denmark Street - tons of guitar shops, and you can haggle them down if need be.
Also about 20 seconds away is Soundcontrol, in the basement below Virgin Megastores, next to Tottenham Court Road tube station (check that map above)
It's the biggest music shop in the UK, and boy are the staff friendly - you can try ANYTHING without feeling nervous/guilty/rushed for time (i once tried an amp for like 30mins..no problem, the staff just leave you to it)
