A few months ago, BA introduced a range of new "online only" fares. I hadn't realised they also covered short-haul; IIRC when I last looked they were long-haul only, but that could be user error on my part.

"Semi-flex online only" appears on the fare selection page, and generally means "change to another flight for the fare difference and no other fees", and "refund for a [IMO fairly reasonable] fee". Typically it's £50-200 more than the base fare.
Fully Flex "online only" is also available (not to be confused with fully flex without the "online only" tag), which allows for refund at any time pre-departure for no fee.

What marks these fares out from conventional ones (e.g. a D code with changes allowed) is that the fare rules aren't linked to the fare code (e.g. I or R) but are in addition. So it is possible to book a fully-refundable long-haul club ticket in I, for c. 25% of the price of a J-category ticket.

The downside is that "changeable" means only within the same fare bucket, so the cost to change is often quite large, particularly if you're close to departure.