Found this info. on the HO website
http://www.workingintheuk.gov.uk
In what circumstances can I request a reprint of an HSMP letter?
01 March 2006
1. Reprinting valid HSMP permission letters will apply in the following circumstances:
To correct errors and omissions
2. You, or your representative, may request reprints of letters from the HSMP Team to correct errors such as spelling mistakes or incorrect details such as mistyped names or dates of birth. Requests should be made in writing and accompanied by the original permission letter. Reprints will be marked 'Duplicate' and will be free of charge once your written request and the original permission letter have been received. If the original letter is not returned your request will be refused and a fresh application, with fee, will be required.
Please note, however, that if you request a reprint to change a detail on the letter of permission that was central to the consideration of the original application then your request will be refused where it is based upon your error or omission. One example of this would be an error in the date of birth, where this altered the consideration from the under 28 years to over 28 years criteria.
To replace a lost letter
3. You may request a reprint of a letter that has been lost in transit. Requests should be made in writing, and contain personal details of the applicant - name, date of birth, and confirmation of the address for posting. Reprints will be marked 'Duplicate' and will normally be free of charge Work Permits (UK) reserves the right to undertake investigations to determine the facts of each case. If the original letter is subsequently found, it must be returned, as the reprinted letter supersedes it.
Requesting reprints of letters that are no longer valid.
4. Reprints of letters issued over 6 months ago will be free of charge, provided that the original letter is returned and all other conditions, as outlined below, are met. If it is not returned then a fresh application, with fee, will be required. Reprinting letters that are no longer valid will apply in the following circumstances only:
Requesting reprints of letters delayed in the post.
5. You may request a reprint of a letter that has been delayed in transit so that it is no longer valid. Reprints will be marked 'Duplicate' and will be free of charge, provided that the original letter of permission is returned together with your written request for a reprint. If the original letter is not returned then your request will be refused and a fresh application, with fee, will be required. Work Permits (UK) reserves the right to undertake investigations to determine the facts of each case.
Where there has been a delay in obtaining entry clearance.
6. You should provide evidence to explain the reasons for delay in this circumstance, and a written notice from the visa section containing the entry clearance interview date, together with your written request for a reprint and the original letter of permission. Work Permits (UK) reserves the right to confirm the authenticity of evidence provided. If you do not provide evidence of the entry clearance delay then your request will be refused and you will be required to submit a fresh application enclosing the associated fee.
Where delays arise from overseas nationals' appeals against Entry Clearance Officers' decisions not to grant leave to enter the UK.
7. You should provide evidence of the delay in this circumstance' i.e. a copy of the successful appeal determination, with your written request for a reprint and the original letter of permission. Work Permits (UK) reserves the right to confirm that evidence provided is genuine. If you do not provide evidence of the delay then your request will be refused and you will be required to submit a fresh application, enclosing the associated fee.
8. Reprints will be free of charge once your written request is received, accompanied by the original letter of permission. If the original letter is not returned, and no confirmation from the British High Commission has been received that they have retained the letter, then a fresh application, with associated fee, will be required.
Hope this helps !!
regards