I'm guessing the next step for you HM will be to fill out the N1 claim form and send it to the courts.
Mr Angry may advise you to send yet another letter with more details in it that may work but ultimately if Yorkshire continue to stick with what they've said (all BS intended to put you off) you'll need to file a claim.
FYI you can do it online at
www.moneyclaim.gov.uk or you can download a copy of the forms and associated guidance leaflets from here:
http://www.hmcourts-service.gov.uk/H...t_forms_id=338
The N1 form can be completed in Acrobat and then printed (but not saved for some reason).
All good reading for you while you wait for Mr Angry’s response
Edit - The
leaflet EX307 gives you a good ouline of the process too.