Big Companies List.

[Turnerman84]

Does anyone know how to get a list of big companies that employ over 100 in a certain region? or how to find companies that employ over 100 in a certain area?

[Buenchico]

No company is obliged to make public the number of employees it has, so there can be no definitive lists.

However simply googling 'major employers xxxxxx', replacing xxxxxx by the name of a county, city or major town might well yield some suitable results. e.g. by googling 'major employers Ipswich' I quickly found this list:
http://www.eadt.co.uk/business/top-100/top-100-table

Joining your local Chamber of Commerce might also prove beneficial with regard to obtaining such information. Membership of the Suffolk Chamber starts at £105 per year.