“Ability to” does not mean a right
Both sides must be in agreement to the contract terms – otherwise there is no contract. That means, on the date you sign the contract, you are bound by the contractual tems and conditions set out within the contract.
It does not in any way mean, you are bound to future tems and conditions untill “both” sides agree to the new contract terms.
Looking at @Oscarmax ‘s contract:
“My contract clearly states 36 lease which can be extended a further 24 months subject to term and conditions. There is nothing in my terms and condition stating I cannot extend only if I fail in my duty to uphold my part of the contract.”
Up until “both” sides agree to the new contract T&C’s, his current contract legally states Oscarmax can extend for a further 24 months, unless he breaks the contractual T&C’s in some way, no matter how may times Motability choose to changes the terms, only will it become binding, if “both” sides agree to the new terms.