Business Visa-Meeting with new company

Guys,

I have a valid 2-years C-Business Visa to the UK, the visa was issued based on an invitation letter from a certain company, I am now intending to visit UK for 8 days for meetings with another company, the questions are:

1. Legally is it ok or I need to have another Visa to meet with the new company
2. If I ill be asked on the boarders about the company i will have meetings with them, should I tell them the original company name that issued the invitation letter or the right company which I will have meetings with them

Please advise as my flight is tomorrow. thanks in advance.