In your current line of work, any sensible future employer will look at your experience much more closely than your qualifications. These days, even job descriptions / HR filters that still say "must have a degree in Computer Science or a related subject" usually add "...or equivalent experience". That's not universally true, but it's true often enough that having experience but not a degree won't close too many doors.
You can check this easily enough if you wish, by looking at some local developer job adverts and seeing how many of them explicitly insist on a degree without adding the "or experience" caveat.
However, if at some point in the future you move to some other career, your software development experience may be worthless; whereas your degree might still be considered to show that you are capable of delivering at a high level, even if the subject of the degree has nothing to do with that new career. (The usual explanation is that a degree shows a commitment to ongoing learning, the ability to complete a self-driven endeavour, etc.)
You are already sensibly considering the time/energy investment of the degree, and how long you want to stay in your location. You don't mention consideration of the actual monetary cost?
A BSc course in the UKEngland will normally cost £9250 a year, though perhaps your course may differ, as it is not full-time study and there might be other considerations. You may also be able to convince your employer to pay some or all of the cost (though in that case they will expect you to stay with them for at least a year after getting the degree, maybe longer, and you'll probably have to pay some of it back if you don't).
Still, if we assume for the moment that you pay that amount in full, your degree will cost you £27750. If - and this is not guaranteed - it helps you get, say, £3K/year more in your next software job (which then compounds into future software jobs), it will take more than nine years to "pay itself off", by which time you will have been a professional software developer for at least thirteen years in total. I am struggling to find a source for the average developer's career length, but I have previously heard twelve years quoted. You may last longer than average, many do; and as noted above, the degree may also help in your second career; but it's a fine judgement.
While I think a degree usually makes things easier for someone to get their first job in the industry; as you have managed that already, going back to fill the gap seems to me to be unlikely to be worth the effort. By the time you have 5+ or certainly 10+ years experience, you'll be a proven developer, and few sensible hiring managers will care about a lack of a degree.