have a gas fire installed and need something to go as a surround tiles are not suitable what can you recommend please

The unfortunate truth is the TV and fireplace are both competing for the same space and any solution is a compromise. Regardless of your desire for a fire it is bad anatomically to hang a TV too high. There is plenty of information online about the best viewing height and viewing distances for different sizes of TV. All this advice is ignored by many people - including professional interior designers. Looking at the design of fireplace you supplied perhaps you could bring a TV into the room and place it on the raised hearth when you want to watch it? My bet is that is the arrangement you would normally live with and then you would remove the TV from your room when you have guests? Or you could put a TV on a mobile stand that you can place in position when you want to watch it? You can get stands that would also take a SKY box or similar. The problem is trailing cables - and where the stand is positioned when not in front of the fire! You can even get devices that enable TVs to rise from the floor but they’re very expensive. Or you could project onto a screen that unfolds from the ceiling. Also very expensive. In my case, I opted to forgoe the fireplace, knowing the TV played a more important part in my everyday life. The room was then designed accordingly. Am I happy with the result? Yes and no but as I said at the beginning any solution - other than a separate TV room - is a matter of compromise.

In place of an open working fire we've installed a Bell Topsham gas fire with closed combustion, within a classic limestone mantel: bloomin' brilliant! Looks great, instant heat, no drafts, no dirt, very efficient. The expense is well worthwhile.

There will most likely be a gas pipe running under the floorboards to that gas supply. You need a gas engineer to re route that gas pipe slightly so it terminates at the fireplace itself (not sure why it doesn’t already tbh). Hopefully this can be done via a cellar or crawl space rather than lifting the floor, however if boards do need lifting it probably won’t be many. Then you need something like a Nu Flame gas fire (like a black box which sits in the grate) as mentioned above. Nu Flame is a good brand, not the cheapest out there but good quality I’m told. Again gas engineer needs to install this.