One tip i noticed whilst ringing my bank is there was a number for customers to ring overseas. I replaced the +44 with 0 and used that instead of the 0845 one - and it worked exactly the same!!

Yes, but you need to be very careful doing that. A number of organisations will see your caller ID is a UK number, and will not answer the call. I seem to recall that there are a number of entries on this forum that suggest you dial the prefix that hides your caller ID first. That way, the call will not show as a UK call. Caller ID between administrations is spotty to say the least - sometimes it "sort-of" works and other times it just announces 'Private Caller' (at least here in the US), so the organisation has no real way of knowing where you are calling from.

Thyere is no problem with FirstDirect who openly publish their 0113 number though they don't give it equal prominence compred to their 0845 number. I have used it many times from the UK. They know you are using it but don't have a problem with that.

Their usage of 0845 goes right back to the 0345 days when it gave a genuine cost saving to those living outside their local area.