Legality (In UK) of setting up a second identity?

Question

Is it illegal to set up a second identity for yourself in the UK if you don't use said identity for anything fraudulent? I know you can change your name to (pretty much) anything you like, but I mean whilst retaining your original identity too and running two lives in tandem.

Can you open a bank account in an assumed name? Assuming you stay in credit and don't run up debts.

Can you apply for a second passport? Assuming you don't travel with it.

Can you rent a house/flat and open utility bill accounts? Assuming you keep them paid.

*This is research for a novel in which a character does after years of running two lives commit a crime on one life then simply disappear to the other so don't need overly detailed answers just gauging feasibility as to whether he is already breaking the law prior to the crime by doing this and likelihood of it arousing suspicion.

Answer 1

No you cannot open another bank account, they will need birth cert, passport, NI number etc.

No to the second as your NI number will show up

Yes to no. 3, but Landlords want a credit history.

UK