If I buy an iPod from USA will it still work in the UK?

Yes, it will be fine.

As stedman says, it will work. A note of caution though.

First of all, the price you see listed in the Amercan online store and in the store itself does not include sales tax, which will be added when you pay for it. (Prices shown in the UK physical and online stores are inclusive of VAT {sales tax} and we pay the price shown.)

Then, when you bring it back into the UK, you must declare it at customs and it will be subject to import duty. I have no idea how much that is. If you manage to buy one online, (and that won't be from an Apple source, because they won't allow you to do so) then once again, when it comes into the UK it will be subject to taxation. In fact, not only you will find that it import duty is added, but the shipper will add their chanrge as well, since they (the shipper) will be collecting the tax from you to hand on to the government.

So if you are intending to buy in the USA in order to save money, be warned that you probably won't.