Pictures are what's needed here. Is it a straight grip Senior, or a slant grip? The linkage parts shouldn't be hard to get hold of either from one of the spare parts suppliers such as Chambers, or even off e-bay. If the rest of the pistol is in reasonable order it will be well worth buying the parts. It could well be that rather than having a non working pistol worth a maximum of £40, you end up with a pistol worth £90-£110+ for the sake of a few quid on parts.
BUT....Pics are a must.
The South of England has 2 good things, the M1 and the A1. Both will take you to Yorkshire.