wandgrudd - Yes - somebody else (in the building trade as it happens) mentioned that there may be steel reinforcements...he also suggested that it should be no problem to mount it here.
marko - good point - I assumed the middle of that lintel (the middle being slightly above eye leveL) would match with the middle of the mount and then the middle of the TV...never occured to me that this might not match as linear as that (it's the standard/tilting mount from chase direct btw).
Either way the bottom of the TV is going to hang below...but I feel this will look really good.
Forgot to ask - I'll also need to place my (what little I have at the mo) AV kit below this...basically the DVD player (which needs replacing

) the Sky box...gamecube...and amplifier (I don't have one for the TV at this stage).
I'm thinking of drilling in two shelves (either glass or wood) into the brick at the back of the fireplace...can't really see a problem with this?
Slight concern over the soot which occasionally get's dislodged from the top of the chimney by either strong winds or pesky birds! It's only a small amount (and there's never fluid/rain making it's way down)...might it be worth putting some kind of 'lid' parallel to the lintel - say a tighter shelve so soot is kept to a minimum? Anyone experienced this?
Many thanks.