You can continue using your singapore account fine, although to top up your account you'll need to use your singapore registered bank card/credit card or buy psn credit for that region online as you won't be able to buy psn cards of that region in shops here. (Sorry if that's obvious or not relevent to you)
If you are planning on buying physical games while here you can still play them with your singapore account, but if you want any DLC for them you would have to have a UK psn account to buy the DLC of the same region.
Most games allow you to share DLC accross accounts on the same ps4 but not all, I think the map packs in COD don't but check for whatever games you are looking at.
You can have more than one account on a single console so that's not an issue.
I think the only region locking with ps4 games these days is possibly China, so you are fine for that. You cannot change the region of an account.