Transport Secretary Patrick McLoughlin said:
I am very saddened to hear that Bob Crow has passed away, and my thoughts are with his family, friends and colleagues.
Like many, I will remember him as a passionate voice for safety on the railways and the wellbeing of those who work on them.
While we may not always have agreed on how to run our railways, he was a powerful advocate who led his organisation from the front and made an important contribution to the debate around the future of rail services in this country.