Well, Citibank sent me another letter today 'Without prejudice Save as to costs' to settle the 'whole of [my] claim'.
So, I could either just accept the amount they offer (800 ukp) or up the anti and re-submit my claim for the full amount and see what they do next.
I think I will send another breakdown of the costs, this time including *all* of the charges to the court, copied to Citibank and see what happens.
I feel a little better today