is it an evergreen variety or a deciduous one?
if its deciduous then I'd just make sure it has plenty of water until leaf fall.
if its an evergreen then give it plenty of water and perhaps a light prune to encourage new leaf emergence in the spring.

Ericaceous compost in generous amounts! An acid loving plant can't take up nutrition well from a pH neutral soil

Thanks a lot It’s definitely deciduous so I’m going to follow your advice and give it lots more water and put ericaceous compost around it - do I need to fork the compost in or just spread it ?

Don't give it loads of water, you're in a place where it'll get plenty of rain water naturally going into Autumn.
Azaleas, rhododendrons, etc. all need acidic soil.

https://www.rhs.org.uk/plants/popular/rhododendron/growing-guide

If its a deciduous one, don't cut it back yet - it might just be the leaves have shrivelled, but the stems are still alive. Give a good soak and generally keep it watered till the weather cools and we're not having any more warm and dry spells, usually late October. You've probably had some rain today, but give it a watering can full (a few gallons) poured slowly on the soil around the base of the plant. If those branches with shrivelled leaves don't produce growth next spring, cut them off then.

If the plant was healthy before suffering drought, don't worry about the ericaceous compost, its unlikely to be a soil ph issue, simply shortage of water. The other thing is, ericaceous compost contains some fertilizer, and its not a good idea to use fertilizer this time of year for permanent plants. If you feel it needs ericaceous compost, use as a mulch around the plant in spring, when the soil is moist and growth is beginning.

It's the W Midlands! There was never a drought there. In July it got to 22°c but there were 8 days in the month when it rained. That's the driest it got this year.
You could do a soil test to check the pH, if it's not around 4.5 to 6 then azaleas won't be able to take up nutrients properly, particularly iron.

Commiserations Sunbeam, mine are in pots and struggling too. We have exhausted the water in the water butts so they are having to make do with a top up of ericaceous compost and some tap water .... fingers crossed for both your plants and mine, and a good downpour before too long!

Filtered light only for this one and maintain the Ph around 6. They have fine surface roots and can quickly dry out; Keep soil moist, but not muddy, adding a few inches of organic mulch will help retain moisture. It needs good air circulation and weed control.

Thank you very much for all the help. Hopefully I can now keep it going!