This morning I took my bike to go to work but realise that when I was trying to shift from the middle ring to the outer ring but the derailleur wouldn't click/stick on it. It would move while I was shifting but when I released the shifter it would return back to its original position. Any clues as to what could be the problem?

I am very much challenged when it comes to the mechanics of my bike so simple explanations / instructions would be much appreciated! Thanks

Sticky/mucky cables (inner and outer) most likely (if everything else has remained the same, and you've not dicked around with it)

the Park Tools site has some very clear and easy to follow guides on bike maintenance including servicing front mechs

Supect the shifter needs some lubrication. Mate had the same trouble. Just attack the shifter with lots of lube and see how that goes.

Hm, not been anywhere mud for weeks really so mud or dirty cables is a bit unlikely. Will checkout the Park Took site though and defo try the lubrication tip.

Stiicky pawl in the shifter by the sound of it, ideally you need to open up the shifter to lube and work it as they're normally at the bottom, out of the way of any spray you can get in through the cable entry.