First of all, thanks lot for your precious advice!!

I had the bike serviced once (not at Evans though), plus I did some basic maintenance on my own: cleaned the chain without removing it, adjusted the brakes a couple of times and changed the pads.

I am afraid shifters need to be changed as that was recommended by the guy who serviced it last summer. He replaced the cables but, as I was told, one of the Revo twist shifters (rear) appears to be knackered. At the time, he also mentioned that I would need to change the chain in the future as it was starting to wear.

I did not check the condition of the chain properly - i.e. by measuring its length - but it is starting to run poorly (skipping teeth) when I am cycling uphill. The local area tends to be a little hilly.

I sometimes cycle to supermarkets to do my shopping and I noticed that chain tends to skip teeth when I cycle uphill, especially with some shopping.

It might just need some TLC, as Contago and pretty much all of you suggest.

So I think I'll go to a local workshop after cleaning it properly and I'll ask them some help and advice.

Again thank you all!!