I had to phone a council today. After listening to ‘welcome, blah blah blah…press one for this, two for that etc and please press the extension number if you know it’ I tapped in the extension number into my new mobile and got this recurring message ‘ the number you have dialed is invalid’.

Must be the mobile playing up I thought - tried again, and again - same message. Curious, I phoned the main switchboard who told me that ‘number invalid’ means ‘the line is busy’.

So now you know…