There are many claimants for the steepest street. Many towns are laid out around a church at the top of a hill so have steep hills leading up through the town. There is no definitive answer though because, as you found, the gradient is not measured unless the street is used by motor vehicles.
The Guinness Record Book lists Baldwin street in Dunedin, New Zealand as the current world record holder of ’steepest street in the world’. This has since been disputed as it was originally listed as having a gradient of 38% but is still listed but with a gradient of 35%. The image below shows this street.
I think the street in your town is unlikely to be 45 as this is a 100% slope and I think it would have to be steps to walk up or down (35% is about 20).
Unfortunately, the Guinness book doesn’t list the steepest road in any other countries, including England. There have been several lists made of the “World’s steepest roads” but none of the top ten are in the UK. Generally, only streets that take motor vehicles are considered anyway.
The steepest road in the UK is usually accepted to be Ffordd Penllech, a one way road (down only) near the centre of Harlech. This is a 34% gradient at its steepest point (on a hairpin bend in the middle) and it is marked 'unsuitable for motors'.
However, there is no clear claimant for the title of ‘steepest street in England’ (Note there is a steepest road but I assume you want an urban street to rival your own).
Some contenders, mostly only claimed by the towns folk themselves~
The last few yards at the bottom of Vale Street, Totterdown, Bristol claims to have the steepest gradient of any road-traffic street in Britain. (In fact, they claim it is the steepest residential street in Europe). This is about 35% slope.
http://www.flickr.com/photos/mykg/2739545542/ Chester's charming St Mary's Hill is reputedly the steepest cobbled street in England. I can’t find any information about the gradient though.
Junction Street in Manchester is remarkable for being a steep inner city road. This is also cobbled and is about a 33% gradient. There's no lead in slope, you come off the level like going over the edge of a cliff, you can't see the road ahead until your bonnet drops down a few feet. It's only short though, about 75 yards.
Old Wyche Road in Great Malvern, Worcestershire, is a very steep residential road, and some say one of the steepest in the country. This is no longer open to traffic.