I've been working in the UK for 15 years and I've always been paid monthly.
As far as I'm aware, monthly paycheques are the norm in most UK companies - everyone I know is paid monthly as well.
The only time I wasn't, and was paid weekly, was when I was only a temporary staff member in retail and had a fixed contract for a certain number of weeks of work (short-term summer and Christmas jobs), but as soon as I went to a permanent staff member at that company, my paycheques became monthly.
When I lived in the US, I actually found it really odd that people were paid weekly or bi-weekly, and not monthly.