Don't worry about getting a fancy, expensive tamper by the way, it's a flat metal disc with a handle. I recommend popping into Algerian Coffee Stores in Soho and checking some out if you can. For me the most important bit (aside from it being the right diameter) is how it feels to hold.
@mmccarthy @>>>>>> @duncs @Tenderloin
Thanks all, looks like Monmouth in Bermondsey is the nearest roaster so will get some beans and have a go! Also ordering a tamper..