Booking WTP out, WT back - UUA outbound?
 

I'm pretty sure the answer is that there's no restriction - but before I pull the trigger on this ...

I'm planning on booking a WTP outbound, WT return journey. The plan would be to UUA the outbound into CW.

I know all WTP fares (except upgraded fares) are upgradable - this would book into T. Question is - would the cheap WT fare (it'd book into O) on the return have any restriction on the WTP fare?

E.g. it's not going to stop me upgrading the WTP fare is it?

(Yes - upgrade availability is there - and i could book and upgrade - but it won't let me do a CW/WT booking through that tool).

Should be fine.
But upgrade ASAP.

This used to be a restriction, but it hasn't been the case for a long time. You'll be fine upgrading the outbound.

I suggest you phone up to book it all in one go as you might have difficulty UUA online anyway given the mixed classes. At least that way you know it is all going to work.

ISTBC but I have been told before by BA agents that they should never charge the telephone booking fee for mixed class bookings as the system does not automatically generate this fee in the pricing.

The service fee should be charged unless there is a problem with the website preventing you to book something which can normally be booked online.