Can someone please explain to me why mobile phone numbers are typically written in a format with 5 numbers followed by a further 6, whereas land line numbers with 4 then 3 then 4?

I don't know why, but it pisses me off. Even more so when people tell me their land line number in a mobile format.

So, why the difference ?

Michael McIntyre does a brilliant sketch on that theme.He makes the point that when others repeat your mobile number you often do not recognise it, so true.
The correct land line format has to be area code (0151) exchange (677) number(1234). So 4-3-4 it is. Mobiles do not seem to have those definitions.

As per post above same works for mobiles.

First 5 numbers used to be unique to each operator. Not as clear cut now due to portability.

Dunstable, Bedfordshire, has dial code 01582.
Fife has 01383
Cambridgeshire has 01223

So the 4-3-4 doesn't work in these cases.

Its strange, isn't it?

4-3-4 doesn't work in a lot of areas, you'll find that most major cities have 4 digit codes (0151, 0121 etc) followed by a three digit and a four.

Towns tend to get five digits, this is a throwback to the old numbers where you could dial one area code for another town that was local to you, and a different code, for the same area, if you were further away from it. Most numbers in these areas are only six digits long, as they tend to be in areas with fewer people, hence fewer numbers.

London is different again, which went from 01 to 071 and 081, then to 0171 and 0181 when we all had the number 1 added to our area codes, then to 02, which is the current code.

Mobile numbers used to be a bit of a mess, and people could very easily call premium rate numbers without realising it, so area codes and personal number codes have now been standardised.

00 International dialling
01 Geographic area codes since 1995 (outside London)
02 Geographic area codes after 2000 (inside London)
03 Non-geographic numbers charged at geographic rates (0300 is Freephone)
04 Reserved
05 Corporate numbering and VoIP (very rarely used)
06 Reserved
07 Mobile phones, pagers and personal numbering (070 are premium numbers)
08 Freephone and revenue share non-geographic numbers
09 Premium rate (PRS)

It can be a bit complicated

its just how its said, all phone numbers contain 11 digits

100
123
999
191
118118
0800 1111 for Childline
0845 46 47 for NHS Direct
Etc.. Not all 11 numbers

ok

MOST NORMAL PHONE NUMBERS are 11 digits long