* Mark Price to leave Waitrose in April
* Says will apply to be Channel 4 chairman
* Rob Collins to be new Waitrose MD (Adds detail, Price, analyst comment)
LONDON, Oct 20 (Reuters) - Mark Price, the self-styled "chubby grocer" who has overseen a two-thirds increase in sales during eight years at the helm of upmarket supermarket Waitrose, will step down next year and will apply to be chairman of public broadcaster Channel 4.
The employee-owned John Lewis Partnership, of which Waitrose is a part, said on Tuesday that Price, 55, would step down as Waitrose managing director and as deputy chairman of the partnership on April 3 next year.
Price, who has had a 33 year career at the partnership, will be succeeded as Waitrose MD by Rob Collins, the grocer's retail director since 2012 and himself a partnership veteran of 22 years.
"The reason I have chosen to go is I have an opportunity now to apply to be chairman of Channel 4," Price said in a statement. His decision to quit was not related to Waitrose recently finding growth harder to come by in an industry besieged by a price war, led by discounters Aldi and Lidl.
Last month, Waitrose posted flat first half profit, with underlying sales down 1.3 percent.
However, industry data published on Tuesday showed Waitrose's sales rising over the last three months.
Friends of Price said he also wants more time to pursue writing and consultancy work. He is currently penning three books, one of which is a children's book.
Price is currently deputy chairman of Channel 4 and has been tipped to replace Terry Burns as chairman, whose contract is not being renewed by the British government.
Analysts at Conlumino noted that under Price's leadership Waitrose added 200 stores, transformed its online business and overhauled its supply chain. Its sales increased by 65 percent and its market share hit a high of over 5 percent.
"Senior management change at the partnership is rather like the regeneration of Doctor Who: it's something that does not happen very often, so is all the more significant when it does," they said.
Price's planned exit means only Asda of Britain's top six supermarket chains -- Tesco, Asda, Sainsbury's , Morrisons, the Co-operative and Waitrose -- has not changed its boss in the last 18 months. (Reporting by James Davey; Additional reporting by Kate Holton; Editing Mark Potter)