Nick.
This would probably be due to airflow direction, for instance if there is a
south easterly flow Brussels would be importing air that had crossed a warm
continent, but on this same airstream reaching the channel coast temperature
modification would take place as it passes over cold water prior to reaching
the english coast. Therefore we would expect it to be noticibly cooler.
However as the summer progresses with the same airstream in place, the
channel would have warmed somewhat so the modification would be less.

Hope this helps. Best regards. Len.
wrote in message
oups.com...
Noticed the repeated reports of very high (for the time of year)
temperatures in Brussels the last couple of days, yet in Southern
England I don't think we've reached 20C. According to the weather
charts no front lies between here and Brussels ATM so I'm rather
surprised. In a typical summer heatwave there's little difference
between Brussels and Southern England, and the quoted Brussels average
max temps (in another thread) of 13C in April and 20C in June are
pretty much exactly the same as inland Southern England... suggesting
it basically has the same type of climate, broadly speaking.

Nick