It's not as simple as it might seem as residency plays a big part. As an example if you work, let's say on a contract based in France, but are deemed by HMRC to reside in UK (a minefield on its own) then you will pay tax and social contributions (high) in France but then HMRC will calculate what tax you would have paid in UK and clobber you for the difference but to make matters worse won't take into account the social contributions you made
All the double taxation treaty does is protect you paying full tax in one country and then full tax in the UK. The only solution is to move to the country of contract if doing so attracts a total tax advantage.