I would have thought a bigger concern should be whether the Inland Revenue starts to take an interest in the heavily discounted travel perks BA crew enjoy.
How ironic it would be if the strikers won some cocessions from BA, but all were considerably worse off if the IR decide to formally count these perks as taxable. Not just ironic, actually quite amusing
I believe that the price of the seat offered to crew is at the "marginal cost" of flying that seat empty, so therefore there is no benefit to either the airline nor the crew person, hence no tax is payable.