MAR and commuting from home or work

My Employer pays (with car allowance) mileage from the office or home which ever is nearest at circa 15p not the 45p, according to https://community.hmrc.gov.uk/customerforums/expenses/2e8f5c18-4ebf-ed11-9ac4-00155d975688?page=1, in a similar situation MAR can be claimed. My question is according to https://www.gov.uk/guidance/ordinary-commuting-and-private-travel-490-chapter-3 section 3.49 as most of the time I almost pass my office circa 5 mins from the motorway when heading south, I could claim MAR from home even though in these instances my employer wants me to treat the journey from the office which is shorter? as south in my instance is shorter from the office. How would this work if I'm travelling from home to a location that's not my normal office, but another location which is slightly nearer to home than my office? I presume this would be treated the same way from a MAR perspective? In that I could calculate the distance from home? I don't stop and work at the office on these trips. Summary, while I only get circa 15p a mile from the shortest distance, is MAR available from home even though my employer pays the shortest distance? Thanks,

Hi Thomas Miles,
It would be based on the journey from home, and you can claim the 30p difference between the 45p and the amount the employer pays.
Thank you.