On 3 July 1257, Ros obtained from Henry III a grant of the free warren, in the lordship of Belvoir, by which the boundary was determined. In 1258, he was actively employed in Scotland, in delivering King Alexander III of Scotland out of the hands of his rebellious subjects; and at Chester, in resisting the hostile invasions of Llewelyn the Last. In the same year, he and his lady Isabel had a controversy with the Prior and Convent of Belvoir, relative to the right of presentation to the Church of Redmile (near Bottesford), which was amicably compromised by their relinquishing the patronage to the convent, for a certain compensation. In 1261 he obtained from the king the grant of a weekly market, to be held at Belvoir, on Tuesday; and of an annual fair on the feast of St John the Baptist, to continue for three days. In 1264, he was one of the insurgent barons who defeated Henry III at the battle of Lewes, and took him and the prince prisoner, confining them in Hungerford Castle. In 1264, de Ros was summoned to the parliament, which was called by the barons in the king's name.