My sympathy has been with the engineers for some time on this one. New contract?, don't like it? do one. I read yesterday that the new contract basically means 3 hours more per week and a lower overtime rate for weekends, I suspect there might be more to it. I'd prefer to see new employees on a new contract and the old timers see out their time on the old contract. British Airways (as a result of covid) have had redundancies and similarly, have been keen to lose the senior cabin staff on 'old contracts'.
On the other side of the coin, British Gas have been heamorrhaging customers for years and seen profits halve over ten years. At 40K a year it probably won't be too difficult to find replacement engineers.