well, I tried -
I break it down to:
1) time spent dealing with the case
2) as a consequence to their negligence - I lost an opportunity to buy a property. So, taking into account the time spent on that, as well as the potential loss in term of mortgage rate / property value / paid rent
3) compensation for harassment - which i define as: they reported an alleged debt which compromised my ability to pursue various financial goals (even as simple as getting a contract with a mobile). They were negligent in investigating / resolving this. So, say, from the point of contact (12 months ago) it should not have taken more than a month. This implies that they are responsible for 11 months.
I claim to have spent about 10 days - communicating with Arrow Global / Vanquis, writing the letters, communicating with you / other advisors regarding the matter.
additional 10 days - reviewing properties online, scoping areas. This time was wasted because Arrow Global did not resolve my case and hence the mortgage application was rejected.
So, 20 days * base current salary * 300% (take it to be a 'consultancy' rate) is ~ 30K
If I could bought the property I would not have needed to pay rent (so, about 6K)
I am not sure whether or not the value of properties has gone up -- if so, and if I cannot get similar conditions for my mortgage , I would like to have this as well. I estimated this by £10K - but I am not sure.
Finally, but quite importantly, is compensation for the stress, dealing with the matter, the humiliation (being refused a mortgage), as well as the consequences - my inability to get basic services and lead normal life. It is difficult to put a price on this, I suggested £50K