Well, I think the majority of the "work" is done in Ireland (for the search advertising - the majority of their revenue), so you're looking at a top-heavy slice in the UK anyway.
Yes, I think your drift is that the stated average of £160000 pa may be misleading. It might be the mean figure (distorted by some multimillion pound salaries) so maybe the median is what you want. If there are around 4000 employees though I think the two figures are unlikely to be significantly different though- unless a few top people earn several hundreds of millions.
I'm just wondering why you're wondering?