Claiming foreign tax credit versus relief under double taxation
 

I am currently completing a first time tax return in the UK due to new (2010-11) dual residence status under the 183 day rule.I was also ordinarily resident in the UK under the 91 day rule for 10-11. For 2009-10, I was non resident and not ordinarily resident in the UK.
I was simply going to claim foreign tax credit on taxes paid in the US however, I came across help sheet 302 for dual residents which explains about claiming relief under the double taxation treaty, this seems MUCH more complicated.
The questions are I suppose ; can I only do one or the other and if so, which is likely to be more beneficial?