I have been talking to my husband about this (27 years experience in Transport Management and qualified to teach Class 1).
He says there is no problem with you taking your class 1 test in Bulgaria (and yes he can teach you!) and you will be able to drive in the Uk with the BG class 1 licence, however, the DVLA will not add your bg licence to your english licence, you would be classed as a foreigner driving in the uk. The DVLA does not recognise any other class 1 licences unless the test is taken in the UK with the Driving Standards Agency to gain the relevant paperwork for your UK licence.
Another point to remember in BG the licence is only valid for 5 years and you would have to renew it here to be able to continue driving in the UK.
If you need anymore information then please let us know and we will do our best to answer any questions.
During the many, many, many…(you get the point) time that Armstrongs teachers get to invest with their customers during a heavy vehicle training course, they certainly get around to asking their customers what they plan to do once they get their certificate.