Rudolph, 25, renounced his intention to play for his country in January so he could sign a three-year contract at Headingley without counting as an overseas player.

ECB regulations however state that to qualify for Kolpak status players must not have played international cricket within the previous 12 months.

Rudolph last played for South Africa in August but the ECB have now been forced to admit they cannot enforce this rule under European law.

The ECB said in a statement: "The England and Wales Cricket Board have reluctantly agreed to the registration as a qualified player of Test batsman Jacques Rudolph by Yorkshire County Cricket Club, having considered all relevant factors and taken account of the legal implications of the Kolpak decision.

"The board in unanimously condemning this type of application are concerned that the registration of players under the Kolpak ruling may not be in the best interests of cricket in England and Wales generally."

Yorkshire chief executive Stewart Regan said: "We are very pleased that the ECB have accepted Jacques' registration and we now have a very strong squad for the 2007 season.

"We understand the ECB's concern about the signing of Jacques on a Kolpak agreement and have confirmed to them that the decision to sign him was not taken lightly.

"We found ourselves in a position at Christmas where we were potentially going to be without our top three batsmen from 2006, who between them scored 52% of our runs.

"Unfortunately, circumstances in December meant we had to look overseas for a Kolpak player. We have reminded the ECB that we are not the first club to sign a Kolpak player and we will certainly not be the last.

"Jacques has committed himself to Yorkshire for three years at the prime of his career and is bringing his wife here who is a doctor. They intend to start a new life and are very excited at the prospect.

"In signing a sworn affidavit, Jacques has given his word that he is serious about his commitment."

Rudolph has played 35 Tests, with a top score of 222 not out, and 45 one-day internationals.

"I am just glad that the long wait is over and I can now make plans to come to Yorkshire," said Rudolph.

"I cannot wait to join my new teammates and start my Yorkshire career. I have been keeping up to date with developments at the club and it is certainly looking good for 2007."