An offset mortgage is interesting proposition - which must take into account your overall objective and your capacity for loss. An offset mortgage is a means of accessing cash as required for whatever reason, loaned against your property, which is being tightened up by the reckless bankers, on instruction of the Government and their current regulator the FCA.
One view is that if you can borrow money at 3 % invest and gain a return of 7.5% after charges - this would appear to be the way to go (e.g Schroders Maximiser). Using the money to fund a pension with 20% guaranteed growth ( IT @20 % ) would also appear to be valuable ( higher rate taxpayers can obtain a further 20 % tax relief ). With a choice of investments in pooled investments or direct share holdings or property investment. It would require a lifetime cash flow modelling to look realistically at the costs, the benefits the advantages and disadvantages - your capacity for loss, and your appetite for such a strategy.
The RPI and the possibility of a bank base rate increase e of up to some 3.5% - over the next five years - and your affordability also needs to be considered. Put simply we would need to take a whole range of information and details to make a considered judgement - before making any recommendation. This is an appropriate product which offers flexibility - but can it work for you, an din your favour ?