Yes. AIUI debit cards use a different number range to credit cards.
Whether companies elsewhere in the world would be able to instantly
tell the difference between a UK issued debit and credit card is
another question.

Yes again- having spoken to somebody who works in the fraud risk
department of a bank, the UK is only just moving to a system of having
the same number of digits in a debit card number as the rest of the
world. Prior to that it wasn't possible to use a UK-issued debit card
for online transactions processed abroad as foreign systems wouldn't
accept our account numbers.