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Kiaora,

Just discovered a bit of moisture in both my headlights. Was not there when I bought it a month back but I fear the heavy rain has resulted in some moisture getting in. The car is a Honda Accord with xenon headlights. Is this something to worry about? I'm waiting for some good weather so I can dry it out completely and go over the seals with some silicone- I do realize excessive moisture could be a WOF fail

If it's just a slight amount of moisture (particularly if it's an even amount in both lamps), it may be just a little condensation which usually disappears within a minute or so when you turn the headlights on and may not be much to worry about. Obviously, if there's real droplets of moisture, that's a different thing and may need to be addressed.
Condensation from cold, damp air can be difficult (if not impossible) to completely avoid. Depending on the year and exact model, headlights often have numerous seals in addition to seals between the glass and body of the lamp, (around the adjusters, bulb holders, wiring, park light assemblies etc).
If seals are failing, they may need to be replaced but I wouldn't apply silicon to headlamp seals as it's not a permanent solution and can cause other problems.
An example of what I'm refering to can be seen here.

Thanks! The condensation is a few droplets right in the corner of the light where it slopes down to the bumper. I took it to my garage at lunch and its apparently a recall fault with the design of the Euro headlights. Honda have fixed this with clips around the seal- which it looks like it has been done on the car. Unfortunately, the workshop tells me that it was only done to the top of the lights which causes the seal at the bottom to give away a bit. The recommendation was to monitor it and if condensation gets worse to replace them with a second hand pair as the new OEM lights apparently never fixed the fault. There are plenty of Euros around so hopefully in the future the lights will be cheaper to replace

My 2 cents worth -
I had considerable moisture in one headlight, fail WoF level of moisture. Tried to fix it, as suggested by mechanic, by blowing a heater on to the light. Worked OK but as I expected it only came back again, within hours.
I removed the light bulb, carrier and rubber boot and left them out for about three days. (Ensuring I only used the car in clear day light). My theory being to allow the ambient temperature and humidity to "equalise" both inside and outside the light.
Did this about four weeks ago and have been clear ever since.