Prime Minister Theresa May said:
Martin McGuinness served the people of Northern Ireland as deputy First Minister for nearly a decade.
We recognise his work over many years securing a number of significant political agreements.
He played a key role in moving the Republican movement towards a position of using peaceful and democratic means.
I want to send him best wishes for his retirement.
We will all continue to work to make sure that the people of Northern Ireland are able to live freely and in peace.