Don’t go to the gym, a waste of time when you are travelling, 2.5 weeks is hardly any time to take off, as long as you do a few heavy exercises in the hotel you will keep your mass and overgrow e.g one arm handstand pushups, one arm pushups, one leg squats “pistols” etc…
Unless you specifically want the gym experience.
Pro-hormones are LEGAL over here, by the way.
http://www.gymratz.co.uk/bodybuilding-supplements/cat2_1.htm
For travel in London, get an OYSTER card as soon as you arrive. You can use them on all transport and for example, a bus trip is 2 pounds with no oyster, and 1 pound with an oyster. So, half price.
There are many free things in London - museums, even clubs that are free entry.
What are your interests?
history - ancient, recent, military
clubs? pubs?
monuments? churches? battle sites? castles?
Most Brits in my experience have hardly even seen their own town, let alone country. Never before have I seen a place where you can stand in front of a famous site, ask a local where it is, and they won’t know. Even the bus driver who drives the route to Highgate cemetary every day, didn’t know where the cemetary was … go figure.
A good cheap meal is a kebab, there are two types - the doner off some kind of fabricated meat, and a shish kebab which is real chicken/lamb, grilled, with salad in a pita bread wrap. It is not that bad. Generally, eating out is expensive but there are some places that are reasonable and good, but hard to find.
More than anything else London is a place where you need to know all the little secret places and tricks.
London has been quite hot past few weeks, rained about 15 days in the past 120 days?
Don’t forget to list your main interests.