Hi
Pdrich's reply is correct, you only ned to grant Power of attorney if you are unable to be present to sign all necessary paperwork.
We gave Power of attorney to our solicitor over a year ago & it has been fine, although the queue for the Foreign & Commnwealth office ( which is just by Trafalgar Square) was very long and you should plan on a days trip to get this done. if you are going to go, plan on joining the queue at least an houyr before it opens, if you want to reduce your waiting time.
It involves getting in a queue, which you are given a number and when called, which is usually a few hours later, you present all the necessary paperwork & pay your fee....they then take this away for about 20 - 30 minutes, call you back & then grant the power of attorney.
I believe there are agencies that will do this on your behalf, for a fee of course, luckily I was fairly local to the FCO & had time on my hands, so it wasn't an issue but if you arent local & the fee isnt extortionate, i'd suggest using an agency for consular services, as it is a rather boring process
I also went for a coffee & bite to eat whilst I waited for my number to come up, which is what most people do.
I hope this has been useful & that all goes well with your new place
Sean