Michael Vaughan has expressed concern about the number of Kolpak players flooding county cricket and reducing the pool of players available to England's selectors.

The England Test captain has become frustrated at the number of players, mainly South African, who have taken advantage of a ruling that no person from a country with a trade agreement with a European Union state should be regarded as an overseas worker.

It has allowed many players to play for counties without being regarded as an overseas player with Glamorgan the only county so far not to go down that route.

Warwickshire's director of cricket Ashley Giles, who is also an England selector, has become so frustrated by the situation he has slammed counties as being "lazy" rather than search for English talent.

Vaughan has become equally irritated by the Kolpak movement, although he believes if the players are top quality they can provide huge benefits to emerging English players.

"I'm slightly concerned about it," he admitted. "There are a number which have obviously taken over a couple of the teams but I can only speak from myexperience at Yorkshire.

"We have two very good ones in Jacques Rudolph and Deon Kruis who have added a lot to the team as well. As much as they can be a negative there are a lot out there who can improve the standards and the training.

"A lot of the young players at Yorkshire are looking up to those two now so I can only speak from my experience and the two we've had have been very good."

But other counties - particularly Northamptonshire and Leicestershire - have hired lesser-talented Kolpak players - a situation which Vaughan believes can undermine England's talent pool.

"Looking around the whole circuit, there seem to be a few who aren't doing that and that's my biggest concern," said Vaughan.

"If they're coming in and improving the standard, playing in the right fashion and training in the right fashion then it can only be a good thing but if they're coming in and not doing that then that's not so good.

"The one thing it does do is make sure you have to be good to get into that XI. If they are quality then it's fine because they add to the standard, but if they're not quality it's like anything they're not going to add to the standard."

Vaughan is soon due to return to Yorkshire to aid their Twenty20 campaign while the one-day side take on New Zealand, but before then he wants England to pick up where they left off and secure victory in the npower Test series against the tourists.

Victory at Old Trafford secured England an unassailable lead, but Vaughan is wary of New Zealand fighting back this week at Trent Bridge and denying them a series triumph.

"I've played New Zealand a number of times in Test cricket and they always make it very difficult," he added.

"I don't think there's ever been an occasion where we've walked all over them from the first morning of a Test match - they're that kind of team.

"They bowl with a lot of discipline, they field very well and at the moment they're batting in an aggressive nature and that's quite a hard combination to play against."

England will go into the Test with an unchanged line-up for the fifth successive Test, the first time it has happened since 1884-5, with Hampshire seamer Chris Tremlett once again missing out on a place in the starting line-up.

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