Hi and welcome to our forums.

If you wish to transfer funds back to the UK, the most economical way might be to use your lawyers client's account (if you happen to have one) and/or a currency exchange company (e.g. HIFX, Moneycorp, Smart Currency Exchange, etc). The former will save you bank wire transfer commissions, as normally lawyers have low or no bank comissions on their clients accounts. The latter can save you in exchange rates, as the 'spread' on their transactions is normally lower than what banks charge (anything from 2.5%). You will have to shop around to find the most competitive rates.

If the amount is above the maximum they accept, perhaps you can try and divide the amount in several transfers, and even use different companies.

Regarding the power of attorney, I don't see a need for one.