Logic path:
Do you want the job back? - yes - Contact the employer asap and explain how silly he's been and he won't do it again and how committed he is. He is then in the employer's hands.
Do you want job back - no - Contact employer to request P45 and final pay. Don't be put off by any nonsense about 'you breached your contract by giving no notice' - as that would be an unlawful deduction of wages. Point that out if the employer tries that trick. (It is a breach of contract but the employer has to pay the wages first, then make a civil claim for damages against the employer for breach of contract - most employers don't bother).
Doesn't want job back - as above, part 2.