First, curse Border Force.
Next, how important is it to you to make your original booking as it is? If you move it, will you move it backwards or forwards, or it is inconsequential either way.
Don't forget that the more important it is to you to make this flight, the more that any marginal cost to you will be insubstantial, whether or not you can ultimately recover such costs or not.
If you decide to ride it out without changing, then you will most likely have a case to move your flight to another one free of charge, though that is likely to happen at the airport in real time (i.e. try to check-in, fail to board, reasons outlined, change granted).
On the other hand, if airlines are told well in advance of the strike and the date is set (no withdrawal of industrial action), then they may offer the facility to change your flight to another one, free of charge (i.e. their normal change fees). This mirrors similar policies for people holding tickets to/from locations subject to natural disasters or conflict. If the airlines offer this ultimately, you may have to contact your agent to make this change, or call the airline to register the change on the ticket which will then put it to the agent who will reissue the new ticket. If an agent receives a change message from the airline and needs to reissue the e-ticket, this is not considered a voluntary change and they cannot charge a fee simply because the ticket changed from what was originally booked.
