The longest & highest would be the Col de l'Iseran from Bourg St Maurice, 48 km at 4.1 % is not steep but you rise 1955 m to 2770 m, the highest paved pass in europe.
I've done the HLifax ones that @Richard A Thackeray mentions, but on a mountain bike with 22/34 as lowest gear. Elland cricket club to Blackley off road is another bit of a tow, as is Copley to The trig point on Norland Moor.
Hardest for me was Wessenden fromMeltham. Unforgiving sort of climb with loads of false horizons and a nasty headwind.
I quite enjoy Cragg Vale, in a smug sort of way.
Its not that bad. The S-bends above what used to be a pub are the danger point on that road.Halifax Harriers have a fell-race around Norland Moor, I've not done it, yet, but want to
http://www.halifaxharriers.co.uk/club/club-races/tour-of-norland-moor/
And, the Stainland Lions 'Bluebell Trail 10Mile', that's the one that goes up Trooper Lane, & back down Dark Lane (amongst other dips & climbs)
http://stainlandlions.com/Club_Races/2014/BluebellTrail/index.htm
How about the climb from Luddenden Foot, up towards Mount Tabor??
. Wow it hurts watching it
3 contenders for me:
Chimney Bank Yorkshire - on a loaded tourer - about 600 feet in a mile
The Oberjoch Pass in Bavaria - easy-ish but long drag - overtook cars on way down
The Schanzenstrasse in Oberstdorf Bavaria - stupid steep and twisty - red hot rims on way down
Its not that bad. The S-bends above what used to be a pub are the danger point on that road.
Is the Beacon Hill fell race still run? Used to go straight up from what is now the main entrance to the Nestle factory.
Brackenbed from Wheatley to Pellon Lane & Windy Bank Lane from Holmfield to Queenbury are worth a go.