Monday I noticed s/he was hanging round the back of the plants when I fed them at bedtime but s/he was a little shy and only recently started swimming more out in the open when I was near the tank.

Yesterday lunch time I noticed his mouth looked like the lips were swollen?? But this time was out swimming and watched him feed ok.

3pm today found him down beside the filter looking "wedged" so I moved the filter and he swam off albeit slowly and hid In the plants.

Just came home and found him upside down eyes White and dead

I started melafix on Monday night just incase as a shot but obviously didn't know exactly what was wrong. He was my fave fish and gutted he's gone.

A very recent pic of him/her.

Constant digging into a coarse substrate (cichlids do enjoy rooting around in fine sand or gravel) can cause irritation leading to swelling around the mouth; in many cases this can result in an infection, either bacterial or fungal. Often fish don't always show external symptoms.

What are your water parameters?

No other fire mouths. He was my friends but she got rid if her tank and I'd had him since January. He was about 3-4 years old.

Water is Ammonia 0.1mg/litre
Nitrate 0mg/ltr
Nitrite 0-0.1mg/lt
PH 7.
temp 24c

No other fish is showing any signs of illness (although neither did he really)

I'd be rather concerned about the ammonia level; it shouldn't be above 0ppm (mg/l.). While 0.1mg/l. doesn't look like a lot, any concentration over 0mg/l. is lethal to fish and the toxicity of ammonia varies with pH and water temperature.

I'd carry out one or two 40% water changes to bring it back down to 0ppm, and cut out any feeding for a day or two.