This dwarfs the money made out of Thomas by his creator, the Rev Wilbert Awdry, and his family.
His son, Christopher Awdry, last year rejected suggestions the family had made as much as pounds 7m from Thomas and estimated the total at less than pounds 4m.
Founded by husband and wife team Britt Allcroft and Angus Wright, the Britt Allcroft group bought world-wide video, TV and character licensing rights to Thomas from the publishers, Kaye & Ward, in the early 1980s. The two founders will keep their combined stake of about half the company. Other Britt Allcroft shareholders include the merchant bank Guinness Mahon and Ringo Starr, the former Beatle, whose voice was featured in the TV series.
Britt Allcroft plans to raise pounds 5m of equity in the flotation to finance international expansion of Thomas and its other brands. In the year to June, the group made a pre-tax profit of pounds 2m on turnover of pounds 11.5m.