The UK doesn't have much of a wet-dry season thing going on, but Spring should be the drier of the seasons. Lack of warmth is one thing, it's when it coincides with endless cloud, drizzle and rain when the (justified) complaints start. People have a right to be annoyed by the first 50 or so days of Spring not being warm AND being dull.
Also just to add for me personally the 1961-1990 is not relevant as I didn't live through it. The average I've partly lived through is 1981-2010, and compared to that average, this Spring has been below average.