Have a look at
http://www.climate-uk.com/temp.htm
There is a marked periodicity in the top (10-day mean)
chart, especially in the westerly index. In previous years
periodicities have come and gone pretty quickly, and I can't
remember seeing one quite as marked as this. It's not a
statistical artifact ... it's easy to remember the westerly
spells in early Jan, early Feb, mid-Mar, early to mid
April, and late May, and also the blocked spells
between.

Philip Eden