IPhone 4S invalid sim help uk?

I've had my iphone for exactly a year and now its saying invalid sim. I've turned the phone of a couple of times but no luck. It's done this before but it got fixed by turning it on and off. What can I do? It's on EE (orange sim)

Get a new SIM

Have you tried a soft reset? By holding down the lock button and the home button together for ten seconds until the apple logo appears? This can sort out loads of problems also you could turn off the phone and take the sim card out, And wipe carefully the gold part and then place the sim card carefully back into place this may also work.
My friends iphone 4 would periodically do the same as your phone and he used the pulling the sim card trick and it would work for him pretty much every time. Good luck.

Also if the problem does persist and you can't get it sorted using the methods i have suggested? Then i would strongly recommend you take your phone to a apple store because even if you did not purchase the phone from there, They will almost 100% sort the problem for you. They are absolutely great like that.

Sometimes a layer of tape on the back of the sim to press it a bit closer to the contacts works

You'll need to see if it's the SIM or the phone.

If you're on Orange, they do not do SIM replacements instore. You'll need to request one by calling 150.In the meantime, try testing it with a different SIM card.

If it's not the SIM that's the problem, it'll be the phone. For that you'll need to return it to where you got it, or take it to Apple.