CGT calclulation - are original mortgage arrangement fees an allowable expense?

Tax Planning and Financial

Hello, I have recently sold one of my btl properties.
I have submitted my draft cgt calculation figures to my accountant.
In my figures I have included an original mortgage arrangement fee of £1300.
My accountnant has informed me that the original fee is not an allowable expense for CGT puprposes.
My understanding was that the orignal purchase costs were allowable expenses - solicitor buying fees, mortgage broker fees and mortgage arrangement fees etc.
My accountant has informed me that the original arrangement fee was an allowable expense against rental income and should have been apportioned over the duration of the mortgage, so for example if the original mortgage was for 10 years then I should have claimed £130 every year on my annual tax return for 10 years.
Is that correct?
Any advice would be appreciated.
Regards
John