andPerhaps Singapore is used as a "Rest area for Subs and crews from the Med.. Send them to Singapore for longer refits and crew rest, or instead move older boats from the UK itself.
Depends on the logistics and equipment needed. Resources to maintain a small subron are one thing. Having a setup where there could be multiple boats coming and going, and taking up space in Singapore yards or drydocks might stretch things. Easier for subs to rest at a safe port in Egypt, or for a lot of stuff faster, cheaper, and more logistically practical to return to various bases in the UK proper as in OTL.
That's one thing overlooked at times, it's not necessarily the boats themselves, it's the ability to supply and maintain those boats so that they're actually usable. It's not just that 4 subs where moved to Singapore, though glossed over ITTL, likely a few dozen or so extra personnel would have needed to be assigned to shore installations in Singapore to help maintain and supply those 4 boats.
Hi Butchpfd, I agree with Viper91 on this, but its worth noting that a lot of the Royal Navy ships operating in the Med were given repairs and refits at Singapore