I have had the odd leak locked by a the A/C drain in the past but in the current hot weather here in the UK I have now got icy water pouring into the passenger footwell. A drive of a few hours in 28C heat totally soaked a large bath towel & left a lot of water on to be soaked up by the carpet. I cleared the A/C drains from underneath but it's not helped at all so suspect that there is something at the other end that is blocked or dislodged. Where do I start dismantling to get at wherever it is that this condensate from the A/C is forming?

In some cases, as in mine car, the drains are clear and "work", but for some reason, they are not exactly aligned, and therefore excess water flows outside of the drain itself.
I explain better: from the heater box there are two plastic pipes, maybe 3-4 cm, at the ends pf the box and at the bottom. From there there is a corrugated rubber section, again 3-4cm, and it connects the "top" pipe with the hoses/pipes that pass through the floor of the car.
Mine rubber sections, probably due to bad mounting of the heater box, are "twisted" and not in a direct line, and present a kink that when too much water is produced by the AC, leaks outside.
Short of stripping everything and realign the heater box - which I will not do - I see no other solution.

To check if this is happening to you, you need to remove the two "cheeks" at the side of the center console, operation I believe is well described in these pages. Once you take them out, you will see the rubber corrugated section around the carpet area. Have fun!

Yep. exactly as Leo says...you cd use something to try and keep top and bottom of the pipe in place... eg a cable tie