The feeler thing is normal - or well, it's as normal as any deformity

It won't affect him. However, he looks bloated and he could be suffering from dropsy - that 'fatness' doesn't look normal. He also looks a little pale and washed out. Is he eating normaly? And do his scales stick out the way the picture is making them look (to me at least)? Could you take a picture from above? It's usually obvious then if a fish is suffering from dropsy.
I tried to find a few pics of what dropsy looks like in gouramies - most are, unfortunately, very severe or late-stage.
http
/www.fishjunkies.com/Diseases/dropsy3.jpg - betta
http
/www.fishhealthpro.com/gvisBZUCHTvoor.jpg - koi (as an example of what it looks like from above) with very obvious pineconing of scales and developing pop-eye as well.
Dropsy is the result of fluid accumulation. It's a symptom - and the root cause tends to be organ failure either because of bad water quality or an internal bacterial (or sometimes viral) infection.
The first thing to do is test your water. Even high nitrAtes are a worry. Then do a water change regardless just in case some kind of toxin has made its way into your water. Don't forget to use dechlorinator.
If there is no improvement, isolate the fish if possible and start medicating with something that says it'll treat dropsy or internal bacterial infections. Make sure to follow the instructions exactly - you must administer the full treatment regardless of any improvements as a relapse is very common.
edit: typo and to add that I also live in the UK and have found King British Anti-Internal Bacteria (I think that's what it's called) to be quite effective.