I’m on the Nationwide Building Society website and when I search for informatin to do with currency exchange, all I can find is information about travel money and they state the total amount of money they can transfer is 2,000 GBP. The Post Office can also only exchange something like 3,000 I believe. I need to transfer a larger sum, 25,000 GBP into Pakistani Rupees. Where Can I go to get this done, and in the future if I need to exchange a large amount of Rupees back into British Pounds, can this be done in the same place? Information needed as much as you can provide. Much appreciated in avance. Thank you.
Thanks for the answers so far. Do you know which exchange rate they would use, their own or the actual rate? And would i receive the rate depending on the time I place the order or would it be determined on what the rate is at the time they deliver the money to the bank?

I understand there is a buy/sell rate when talking about currency exchange; is this so?