Ignoring the obvious distinction between a Brit and someone from England...

I have never seen 1,5 used in the UK, I was always taught 1.5 which I say as "one point five".

Now, the French are a different kettle of fish altogether, I always thought it was they who used a comma in place of a decimal point.

We use commas to indicate groups of 3 digits in large numbers, eg. 1,234,567.8 is "one million two hundred and thirty-four thousand five hundred and sixty seven point eight" At least it is as far as I was taught, (non-English) Brit that I am

We don't swap millions and billions either, but historically, a billion over here was one million million, not one thousand million. We pretty much accept the smaller value now, but if you were a proper billionaire in the UK, suffice to say you could buy Bill Gates before breakfast and still have change for a decent lunch in the Dorchester