Honestly, do it by hours of light in the day.
The UK is pretty far north. In fact Yorkshire is about where Edmonton is (latitude wise...or is it longitude..?)
In the summer you can get a LOT of daylight. Shooting intil 9 or 10 wouldn't be odd in some parts of the UK. So, go on-line and find the sunset-sunrise times for that area and go from there.
The Dales are just amazing. Especially when the heather is in bloom. Something to look up too. I recommend Whitby very highly. Very picturesque, if touristy at times, town.
And, as has been mentioned, the weather is crap shoot any time of the year. You could have an awful spring, or an amazing one. Same for late summer.
And any other time of the year....
Then again, I have seen winter days in England in December that are just breathtakingly clear and beautiful.
Followed by rain....