Michael Vaughan's return to captain England in the second Test against New Zealand today could be interrupted by an emergency dash up the motorway to witness the birth of his first child.

Vaughan's comeback after missing the opening Test victory at Lord's with a knee injury has dominated the build-up to the Headingley clash.

He confirmed yesterday he will return to the side at number four, allowing Andrew Strauss to continue at the top of the order and build on his impressive debut in the first Test.

That return, though, may be temporarily interrupted, with Vaughan revealing that he may disappear at a moment's notice - providing he is not batting - if he receives a call from wife Nichola, due to give birth at their local hospital in Sheffield any day now.

Vaughan's dash down the M1 has only been possible because of New Zealand's generous attitude to the situation after they have agreed to England's request for a substitute fielder in the captain's absence despite there being no provision for childbirth in the Laws of Cricket.

But while the tourists were happy to accept England's request for a substitute, they were not prepared to waive the laws which state that if Vaughan is absent for a considerable length of time he would not be allowed to bat any higher than number seven.

Should that happen, it would halt England's plans for the new batting order in which Vaughan had hoped to settle into his role at four, a position which has become vacant following Nasser Hussain's retirement last week, and allow him more time to concentrate on his captaincy than he would have as an opener.

Vaughan revealed: ''It's been in our thoughts for quite a while.

''We've discussed it over the year and we've finally found a really good replacement to go at the top of the order.

''Nasser's retirement has opened up a place at number four and it's the perfect time for me to slip down there and let Andrew Strauss continue to open the batting."

Critics of Vaughan's demotion would point out that he has scored ten centuries in his 31 Tests as an opener, briefly held the number one position in the world Test batting rankings and averages 49.70 at the top of the order.

By contrast his record at number four is less impressive and he has a far more disappointing average of only 26 lower down the order.

England will make a decision this morning about whether to continue with left-arm spinner Ashley Giles or play Durham's Paul Collingwood as an extra batsman although the seam attack comprising Steve Harmison, Simon Jones, Andrew Flintoff and Matthew Hoggard is expected to remain unchanged.

England (from): MP Vaughan (captain), ME Trescothick, AJ Strauss, MA Butcher, PD Collingwood, GP Thorpe, A Flintoff, GO Jones (wicketkeeper), AF Giles, SP Jones, SJ Harmison, MJ Hoggard, MJ Saggers.

l Durham duo Nicky Peng and Gary Pratt will share 12th man duties at Headingley.

l Captain Stephen Fleming yesterday gave New Zealand another scare ahead of the Test. Fleming awoke with an ear infection and missed the tourists' final net session. The New Zealanders already have concerns over Craig McMillan's broken finger and Jacob Oram's side strain.

Fleming, 31, has missed only three Tests since taking over the captaincy seven years ago.