Not surprisingly lb and heypresto consulted the same erroneous source. It seems to be only this group of solicitors (OTS Solicitors) who can't spell. There is no way that BMP is an abbreviation for Biometric Residence Permit, particularly as the official abbreviation is BRP Biometric residence permits (BRPs). I checked Google Translate, but the nearest I could get in Welsh was TBB.
Welsh_Sion, perhaps you could tell us where you found it?