A big thank you to all for the replies to my coolant leak problem. The suggestions enabled me to fix the problem myself avoiding more mechanics bills!
Diagnosis - It was the coolant pipe that feeds the cabin heater matrix as ‘norkep’ suggested.
It was leaking at the point it connects to the back of the engine block at the top. i was able to see it leaking down the back using my girlfriends make up mirror and a torch.
It was bitching to remove because it was very difficult to get some pliers on the clip at the back of the engine, but it’s almost worth the pain for the satisfaction of finally removing it. In hindsight I wish I had just chopped through the clip instead of using pliers.
I got a new pipe from Lexus Hatfield for £20 and put jubilee clips in the place of the original tension clips. I used a jubilee clip with a wing nut for the engine block side.
Norkep was right- you have to be very careful with the heater valve side of the tube-Its very brittle- I broke a bit off the end, but luckily it seems ok.
I hope this thread helps someone because the location of the leak makes it look like its coming from the engine and a very expensive problem to fix( for an amateur mechanically minded owner) ,when all it takes is £20, a couple of days of backache and loss of some knuckle skin.