It is very hard to hold your position on first page. For that you need some one who dedicate with it and constantly monitor it and maintain it. That you can get from seo services Provider Company or Seo consultant. And it is advisable.
Interesting take,my experience is that you can hold your position for many years.
Stable positions is the goal with SEO at least it should be -- especially with regional results that you are looking for i.e. manchester should be achieved pretty quickly.