ITV has acquired Mammoth Screen, the independent production company behind highly rated shows such as Poldark and Parade's End.
By tripling the 25 per cent in the stake it bought for £1m in 2008, ITV has acquired the full business which is "one of the most impressive and sought after drama producers in Britain" according to managing director Julian Bellamy.
Mammoth's high-end drama productions, such as Poldark and the award-winning Parade's End - a joint production with HBO - have often drawn critical praise.
The first season of Poldark enjoyed an average UK audience of 8.2m, persuading broadcasters in Australia, the USA, Sweden and elsewhere to buy its rights.
Mammoth co-founder Damien Timmer commented:
This move will allow Mammoth to make even more ambitious drama, working with the best creative talent in the business. We have a long history with ITV Studios, and with its support and backing we'll be able to make television for a wide range of partners both at home and abroad, whilst remaining a very British television company.
As part of the original deal, ITV's distribution business has had an exclusive distribution for all Mammoth Screen productions since 2008.
Chief executive Adam Crozier wants to make the company better prepared to deal with falling advertising revenues by buying and creating content that can be distributed to big international marketplaces as well as "scripted projects" that can deliver high-end content.
Drama shows such as Poldark, Downton Abbey and Titanic have all been big winners for the company in recent quarters.
An exact figure for the value of ITV's acquisition of Mammoth was not provided. The producer is expected to report a turnover of £24.3m for the year ended October 2014.