Yes he can, but with one big disadvantage. He cannot receive any benefit from the will - this means he will not only lose any legacy he has been left in the will, but will also have to pay all fees and expenses in getting probate out of his own pocket - he cannot reclaim them from the estate.
Sorry, but I disagree with you dzug. Yes he will lose benefit of a legacy under the will, but he will not have to pay for the privilege of getting probate. Reasonable out of pocket expenses are always refundable. However, he would not be able to charge a fee. That used to be the case, until the Trustee Act 2000 was enacted. s28(4) now provides that an executor (in certain circumstances) can claim remuneration irrespective of whether he has witnessed the will.