I doubt that a wheelchair ramp can be installed for the steps at the Boots-end of the underpass. I haven't measures the height of the stairs, so I cannot say definitively, but in view of a maximum gradient of 1:12 as required by building regulations for a wheelchair ramp, I don't think that a straight ramp could be constructed in view of the headroom. Further, a ramp using switchbacks would take up nearly all of the width of the stairs.

I would urge you to explore whether or not a ramp can be installed at the site before asking people to petition for it.