There's this on ABA banking. I never used it so far. May be worth a look!
https://www.ababank.com/en/personal/mon ... transfers/

Set up a PayPal or CashApp account in the UK, or any other non-bank money service that can accept small payments.
Then send yourself an invoice to another email address and pay it with an ABA or other Cambodian debit card. Just email yourself a Paypal bill and settle it with a Cambodian card. This usually costs around 3-4%. Then withdraw the funds from Paypal/Cashapp to your proper UK bank account. This is usually free... I use both and works great (but only for small amounts).

If you have a registered business and have a business bank account, you can also set up a merchant account to accept credit cards online and charge your ABA card directly (just 2-2.5% fee). Just send yourself an invoice and pay it. There is a 14 days delay before the funds hit your bank account though. But I think it's the cheapest way.

Usually, the problem is sending small amounts the other way round, from the UK to Cambodia...