I know after I wash mine, water runs through the hood where the centre vain is mounted.
I know you said it was in the garage though, but that's one way it does happen.
If you washed it, then water will and can accumulate there.

If it's a coolant leak (very unlikely) it's pretty easy to determine if it's straight water or an anti-freeze mixture.

EDIT:
You should read up on how carburetor's work, specifically the SU's.
They are incredibly simple things, even more so then the fixed jet North American counter-parts.

Start with how a venturi works and its relation to atmospheric pressure.
Carbs work on the same principal.

 

They are very simple. You should take a look at the SU pamplet here

JCNA Publications | Jaguar Clubs of North America

I bet we have issued 10,000 of these over the years.

 

Many thanks for this chaps, I had washed it about four days previously but never had water collect at the plugs before, only if I have opened the bonnet before fully drying it.

 

You can find the SU manual here if it helps

Resources

 

To be honest it looks from the diagram as though the fuel has got past the needle assembly but the plunger is in the closed position so the fuel has built up and was forced up the intake passage as it had nowhere else to go. I will get a chance to go over things at the weekend.

 

For the fuel to get that high, the float chamber has to be flooded, so go back to basics and check the float chamber, ensure the float is actually floating, check the overflow pipes are clear, and see what the level in the chamber is.

If fuel spills out when you loosen the top, then the chamber is flooded, at that point either there is detritus in the float valve, the valve is shot, or the float is not floating or is sticking.

You will have to turn the ignition on for a few seconds to fill everything up then do the checks, if you check after it has been stood for a few hours you will not get the right diagnosis.

 

Thought I would update everyone who helped with my problems.
The starter motor had two issues, first one was the nuts were only finger tight and second it had water in it from a leaky inlet manifold stud directly above. Was impossible to get out with carbs in situ so luckily they were being removed. Fitted a WASP starter which had studs attached and connected from the rear instead of the front so easier to remove next time. Second issue was the leaky carbs which turned out to be a sunken float, it had just come back from a rolling road tune up who had just backed the other carb off to compensate the over fueling front carb. Nice work guys, nothing like doing a solid job and that is nothing like doing a solid job. The water around the plugs had come through the centre chrome strip when it was last washed so thats a lesson learned. The Helicoil situation had to be sorted, so we removed the head and sent it to a firm in East Dulwich who did a grand job, they also found a damaged exhaust valve which explained a lot. Although not what you want from a newly rebuilt engine but such is life.We are still having to sort others mess out be the worst is now over. Anyway head back on car, apart from slight leak from offside oil banjo bolt all is good and was dyno'd last Wednesday and now running as she should of been a year ago, so thanks to all who offered advise and to those who are just starting down this road my advise would be to stick with it as it will be worth it in the end.
Almost there now, just in time for summer.

 

looking very swanky I must say, well done for persevering, such a shame that sometimes you don't get the service you expect.

 

Jewelry.