Rt Hon James Brokenshire MP, Secretary of State for Northern Ireland, said:

I am sorry to hear Martin McGuinness has decided not to stand for another term in the Northern Ireland Assembly, and have spoken to him this evening.

I thank him on behalf of the Government for his work in securing a number of significant political agreements, as well as his service as deputy First Minister of Northern Ireland.

https://www.gov.uk/government/news/secretary-of-state-statement-as-martin-mcguinness-confirms-he-will-stand-down-from-politics