Sorry, a bit long, but trying to give all facts. Thoughts & advice much appreciated - please excuse my lack of knowledge/experience.
Engine is 1.6 K series (140 supersport in case that makes any difference - suspect not).
The short story: I seem to have sprung a coolant leak. As best as I can tell, it is from around the coolant rail on the side of the engine, around where it joins the engine.
The long story: On last day of Wightblat (terrific weekend - thanks all for organising and for all the great people met while there) we decided on a trip to The Needles. On parking up we noticed a few spots of something on the ground pretty much over the last 5 metres or so that we drove. No sign of anything dripping under the car, and all levels looked okay, so filed for future checking - thought at time that it might not have been us. But on leaving the car park the engine temp went higher than normal for probably 20-30 seconds, then very rapidly dropped to normal 80ºC. It stayed there with some very slight wavering until we reached the ferry. So in my head I was thinking "stuck thermostat"/"airlock", although had a nagging doubt about the fluid. We got off the ferry fine, and everything behaved perfectly normally for the 50 minute or so drive home, including through the Lyndhurst queue. We could hear the fan operating normally (ie kicking in and out) in the queue, and when we got back home. But after unloading the car we noticed a few drips on the garage floor, and looking under the car revealed a significant pool of what turned out to be coolant. There were also a few drips on the drive where the car had been idling while I opened the garage, but absolutely nothing on the road outside, including where I had turned round.
So it seems I have a leak that appears to only occur when the car is idling. Current theory is that the leak occurs when the coolant is hottest (ie fan running), and hence the system is at highest pressure. Does this seem likely and reasonable?
Diagnosis of leak around coolant rail is based on some trace of dried coolant below this point, which is also where there was most splashing when the original puddle found, and underside of rail found to be wet near connection to engine, when everything else is dry. I assume there is a gasket of some sort between this rail and the block - is it easy to access and replace? Or is there some other potential explanation?
Unclear now how much coolant is now actually left in engine - expansion tank shows level at minimum mark, but bleed tee near heater is empty.
So, a service is due anyway, and I was planning on giving Tom New a call in the next few weeks. My thoughts are just to get him to have a look and fix whatever the leak is while he has the car. My plan to get there is to use breakdown recovery service. However a friend (who is neither a 7 owner, nor a mechanic, but technically savvy) suggests that provided I top up the coolant, do a pre-check to ensure it only leaks while the fan is running, and carefully monitor the temperature, I should be able to drive over to Tom (unlikely to need to stop for more than a few seconds at a time on way). Is this wise, or should I stick with my plan A?
Thanks for all advice and thoughts.