Terry Harper wrote:
"Richard J." wrote...
Mrs Redboots wrote:

Really, of course, we should quote London numbers in the same way
that we quote every other number (mobiles included) - as a group of
5 followed by a group of 6.
snip
Also, I certainly don't adhere to any particular grouping of mobile
numbers, preferring to group the digits in the most memorable way. Do
any of the mobile phone companies or any other relevant body recommend a
particular format for mobile numbers?

I find them much easier to quote as, say, 0791-234-5678. The only
recommendation I've seen is to quote them as +44(0)7912345678.

....Which looks utterly stupid to me, as here we bracket the area code as
an alternative to including the country code.

IOW your example should either be
(0791) 234 5678 or
+44 791 234 5678