Travelling to Canada from the UK?

I know that i do not need a visa to enter Canada as i am a british citizen with a british passport. But if am staying for more than 90 days do i need a visa? e.g. no longer than 3 1/2 months

You will want to check with the high commission or canadian embassy, but in most cases no, unless you are going to work or study over here.

When you arrive in Canada, the immigration officer will decide whether you can be admitted to Canada and, if he/she is satisfied that you intend to stay only temporarily, will decide how long you are allowed to stay. Unless otherwise specified, you are authorized to stay up to six months. You must leave Canada by that date or, if you plan to remain longer in Canada, at least three weeks before that date, apply to prolong your status.

Most tourists when they enter Canada are given a 'temporary resident status' which is stamped in their passport and is usually good for 3 months. If it is not stamped - then it's up to 6 months.

The Citizenship and Immigration Canada website (CIC) has some great information about visiting Canada either as a tourist, student, temp worker, etc.:
http://www.cic.gc.ca/english/visit/index.html

This .pdf document Extending Your Stay In Canada contains a government call centre number, what form needs to be filled out, where to be mailed, costs, etc.:
http://www.cic.gc.ca/english/pdf/kits/guides/5551E.PDF

Ah, government paperwork, you've gotta love it! Good luck!

Cheers,

Petra M, Vancouver

you have to apply to extend your visit and you must send application i month before your time is up. it will cost around 75 dollars
http://www.cic.gc.ca/english/applications/index.html