This is a warm weather plant for zones 8-10 USDA. That's Texas, Florida, Hawaii, Puerto Rico. It is very sensitive to cold/cool and wetness. It should have good drainage and let the roots dry out between watering. Also in those states the sun is more intense with longer days. I feel the yellow marks you see are related to these issues.

At the moment it's in a non heated conservatory it started life in a small pot that dried often so i repotted it. So I'm no closer to finding out the reason i will just keep trying different things i guess but it does grow outside in u.k. if given protection in the south of the country.

I hope you do soon.

I wonder if it is a virus.
other alternative could be damage from the sun shining through glass onto the leaves

have you fed it recently?

Yes someone else suggested sun scorch which it could be my conservatory has an obscured roof but clear glass windows so there is chance it got caught. Anyway it's unlikely that we will get much sun now for a few months. Otherwise it's a virus.