Manchester United's new co-owner Jim Ratcliffe said the English giants have much to learn from "enemies" Manchester City and Liverpool as he echoed Alex Ferguson by vowing to knock the pair "off their perch" within three years.

Ratcliffe, 71, completed the purchase of a 27.7 percent stake in the club on Tuesday, but the terms of the deal will delegate control of football operations to his company INEOS as he seeks to rekindle United's former glories.

City and Liverpool have been the dominant forces in English football over the past decade, while United's fortunes have faded since celebrated former manager Ferguson retired in 2013.

Liverpool sit top of the Premier League and could move level with United's record of 20 English top-flight titles at the end of the season.

City have been champions for five of the past six seasons and this term they are aiming to become the first English side to win four consecutive top-flight titles.

Ferguson once described City as the "noisy neighbours" during the early days of their reign under Abu Dhabi ownership that has transformed the club's fortunes.

And he previously said his task when arriving at United in the late 1980s was to "knock Liverpool off their perch" after a period of dominance by the Merseyside club.

Both phrases were echoed by Ratcliffe, a self-proclaimed United fan, when he told reporters on Wednesday: "We have a lot to learn from our noisy neighbour [City] and the other neighbour [Liverpool]. They are the enemy at the end of the day.

"There is nothing I would like better than to knock both of them off their perch. Equally, we are the three great northern clubs who are very close to one another."

Ratcliffe has already got to work in trying to overhaul some of United's failing structures off the field.

Omar Berrada has been poached from City to become the club's new chief executive and Dan Ashworth has been put on gardening leave by Newcastle as United try to finalise a deal for him to become sporting director at Old Trafford.

But British billionaire Ratcliffe pleaded for some patience while he attempts to restore United to the top of English and European football.

He has plans to either redevelop Old Trafford or build a new stadium as he admitted the 74,000 capacity venue has "fallen behind" the homes of other leading clubs in the past 20 years. (AFP)