I would say a Senior iPhone Dev in London would be £60k+ but since the number of com's who need ObjC is pretty small (even though London has a lot of Mobile dev's) then I wouldn't be surprised if it topped-out at £50k.
In London, a £75k job is very well paid, even in finance, therefore a £100k job (I assume you meant $160k) is getting into higher-management or Contractor territory, not Senior Dev.
