Officially you should get, for base points, 10 per $
At the current exchange rate of $1.64 = £1 (google) you'd think you got messed over.

However, the rate should only be on the rate excluding taxes (i.e. excluding VAT at 15%).

As such, London rate excluding VAT: ~£107.82 should have given (@1.64*10) ~1768 points base

And Bristol excluding VAT: ~£367.64 should have given (@1.64*10) 6029 points.

As such, strictly speaking neither is correct.... for the first they've forgotten to remove the VAT element and using a worse rate, for the second they have calulated it properly but it looks like either a worse exchange rate or they've forgotten to add the amount from the food+drinks. (Excluding food and drink @ 1.64 it comes to 5582 points)

Up to you if you'd like to take it any further... of course they don't retrospectively check any other claims apart from the ones you make as far as I'm aware so you could only complain about the one that doesn't benefit you - but I'd resist telling them about the one where they gave you too many

PS: This assumes that by referring to 'base' above you really are removing any other benefits (bonuses or welcome gifts)

PPS: I stay in Marriotts primarily in the UK and treat the points as a random game... they are frequently wrong and the exchange rates are obtuse - I think on the balance I end up ahead, but on some stays I'm certainly down. Then again I had one hotel giving me $2 to a £1 for months after the exchange rate collapsed last year.