I have put a 5 foot light in my attic.I have connect 3 core flex(brown /blue/earth) to light and have a plug top on other end.So basically if I need to turn it on I just plug it into a socket in the landing.But I want to connect it to an existing single pole light switch and lose the plug top.how do I do this?

What does the switch currently control and where do you live?

A bedroom light.Ireland.

Is the wiring between the switch and the bedroom light accessible? If I were to say "switch loop" would you know what I mean?

The switch is accessible,yes.If I run the flex to the single pole switch and get a two pole switch,use the brown as 'common' and the blue as neutral and connect it to L2 on 2 pole switch,will it work then or will I have to use a jumper/link between L1 and L2?

Sorry misread your question.Yes the wiring is accessible ,via the attic and no, I don't know what a switch loop is?enlighten me...

Not sure how much Irish wiring is like in the USA but think its similar. Only one wire comes into a switch and then one leaves hot. If you have no second wire coming into the box you have no neutral. If you can get to the wiring at the bedroom light that one wire will enter the box along with a neutral. If you connect to the neutral and the hot you can run a cable to your new attic light. What Is A Switch Loop?