My Dad is going to California soon & by getting it (the 60gb Video in black) there I can save about £70 / $120.
I doubt that's possible. US Price is $399. If you buy in California you will HAVE to pay a sales tax of around 8% or more (I believe). That would make the final price about $430.92. The current dollar/pound rate is about $1.75=£1. So, that would make £246 for the UK version. But unless your dad trades foreign currency, he won't get that rate - credit card companies take a lot of it. So there goes another 5%. Your saving is now about £30 on the UK street price. Then just hope your Dad doesn't have to pay VAT and duty on it when he brings it through customs and declares it (as he should!). Then it will be more expensive!
And you won't have the same warranty you get in Europe, and may find it harder to deal with if there are problems.
Sorry to spoil the party, but these days the differences aren't much - it's basically down to UK VAT (17.5%). When you accept this is INCLUDED in the UK price, whereas Sales tax is EXCLUDED on the US prices, it's a lot closer.