NEW DELHI: Former England captain Alastair Cook came up with an idea that could give Test cricket a new shape, as it may help the bowling side take all 20 wickets in a match.

"A new rule I would add would be how about, in 160 overs, you can take the new ball whenever you want?" said Cook, while speaking with Michael Vaughan, David Lloyd and Phil Tufnell on The Overlap and Betfair's Stick to Cricket show.

"You've got two new balls for those 160 overs, and you can take that second ball whenever you want. You could take one after 30 overs if you wanted to."

Currently, the fielding captain can request a new ball every 80 overs in Test cricket, but Cook's suggestion could help the bowling side make early breakthroughs.

Former England captain Vaughan supported the idea of using substitutes more freely, beyond the current rules that allow them only for concussions or other specific situations.

"In the first innings of the game, like-for-like, Rishabh Pant at Lord's is the perfect example," explained Vaughan. "He takes a knock to his left hand, so he can bat but he can't [wicket]-keep - Dhruv Jurel comes on and keeps for him.

"You can't spend the whole game off the field, not fielding and then bat. Nathan Lyon at Lord's in the last Ashes popped his calf early – is the game worse off for losing a player early in the game?

"We have concussion subs, so if somebody gets hit early on the swede, you can replace that person. So why don't we have substitutes? All of the other sports have it - why are we allowing the game to be reduced in quality if someone gets a clip.

"The key to it will be an independent doctor on-site, but the independence will be very difficult to manage. But I think Test cricket now should have subs.

"It's got to be a serious injury - it might have to be if you've got a bone break. Or you have to have a scan to prove. Nathan Lyon had clearly popped his calf badly and he's not going to play any part in the game. Should Australia have had a sub that day? I think so.

"It was Matt Parkinson who played for England as a concussion replacement for Leachy (Jack Leach). That happened because Leachy got a blow on the head. If we're having concussion subs, then why don't we just have subs."