Your Nepali cards may not work at a UK card terminal, and opening a UK bank account can take one to three weeks after you arrive. Plan for that gap.
In small notes (£5/£10/£20). Enough for transport, a SIM, first groceries and a deposit while your bank account is still being opened.
A multi-currency card (Wise / Revolut / a bank forex card) is far cheaper than exchanging cash. Test it works before you fly.
Otherwise the first foreign transaction gets blocked.
For the taxi home if a flight is cancelled, and for your return.
Someone at home who can send money the same day if needed.
Giffgaff / Lyca / Smarty SIMs can be posted to your UK address before you arrive, or use an eSIM on landing. Airport SIMs are overpriced.
Get this done in Nepal — free there, a hassle in the UK.
For the journey only.
Family, university international office, Nepali Embassy London, insurance hotline — on paper, not only in your phone.
Declare large cash
You must declare cash of £10,000 or more (or the equivalent) when entering the UK. Undeclared cash can be seized.
Carrying that much is inadvisable anyway — transfer tuition and living funds through the bank.