That sounds rather similar to what happened here. At 18Z the
temperature was 27°C with a light and variable wind and a few minutes
later the wind became a rather gusty ENE'ly, about force 4, with the
temperature falling 9° in an hour.
It happened about 16:15z here in Leysdown (north Kent) - there was a sudden
gust of wind and the temperature fell sharply, 6C in the half hour between
16 and 16:30z. There was also an appearance of some cloud, although the sun
came out again by 17z.

The hourly summaries for Southend show it well:

http://weather.noaa.gov/weather/current/EGMC.html

Interestingly, the MetO picked up on it rather well, showing the wind
veering and temperature dropping markedly between 15z and 18z for here. GFS
had a similar switch but a smaller drop in temperature.