Having arrived this summer my son (18) is considering returning to the UK to do a degree course starting next year thats not available here (Motorsport Engineering)

Does anyone know whether time away for study counts as absence for maintaining premanent residence status or citizenship ?

Yes it will.

But a three year degree, with a couple of trips back to Canada during the vacations should mean he keeps his PR at least, even if hes not making any progress towards citizenship. If its the one at Brunel its probably a sandwitch course.... 4 years, which would be too long away to keep PR.

What would the implications be regarding fees in the UK? I'm thinking overseas tuition would apply...

What are the employment prospects in that anyway...Im thinking its very specialised for general engineering jobs, and that not many of the engineers at McLaren, Ferrari etc have such specialist first engineering degrees either... Most probably have either extensive experience or higher degrees...or both.

Chances are your son will have to pay the overseas tuition fees, which are very high, as you are all no longer resident in the UK and not even in the EU. Be prepared to factor all those additional costs into your budgeting. Usually at least three times normal costs for an overseas student.