Still on mortgage of previous home

[AVC1978]

Hi
Any advice gratefully received as my conveyancing solicitor appears unable to answer...
I joint owned a property with my ex-partner, I no longer live there but am still named on the mortgage. Due to his earnings our current lender will not lend him enough on his own to remove me from the mortgage. He now has a pay rise and I should be able to be removed from the mortgage in 3 months.
My ex partner has bought me out of our old property so I have no interest in it other than being named on the mortgage.
I am currently buying a new property which will be my main residence. Do I need to pay the higher rate of SDLT and if so can I reclaim once removed from my old mortgage? My solicitor says technically the guidance says my old property must be sold in order for me to reclaim. I'm not sure if I should pay in the first place .

[maths]

To be exposed to the 3% SDLT charge requires at the time of purchase of a residential property (ie "completion") that the purchaser has a major beneficial interest in at least one other property (worth at least £40,000).

It seems you have no such interest in any other property (your ex having bought you out). Remaining on the mortgage is irrelevant.