Formal use of 'pound(s) sterling'

[Tamara]

Hi

I know that pounds sterling is very formal, but I need to know,
would six hundred and twenty thousand pounds sterling (writing in words) be correct?

(Tag question :) )
Does the phrase To convert money in pound(?) sterling requires the plural form?
Or the singular form can be (also?) used – for example, this way:
'To convert money in Pound Sterling'? (..into... ?)
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[Mister Micawber]

.
I'm not Brit, so I cannot answer your PS questions, but I think it is convert into. In AmE, it would be convert into dollars.
.
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Native English teacher at Mister Micawber's

[Conchita]

I'd say convert/change into pounds, pounds sterling or sterling ('sterling' is an uncountable noun).

[Tamara]

A million of pou... thanks!
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It’s impossible to learn swimming without entering the water…