This is the medical certificate that states that you are fit for work or not. All commercial ships in the world have the same ILO standards and MCA has their own (following ILO) format that is called the ENG1. In case you live abroad you need to find a Doctor that is MCA (Maritime Coastguard Agency (UK)) qualified.
Examining the MCA site one can find listed all MCA qualified Doctors in the world that are entitled to issue MCA ENG1 medical certificates. Any other Doctor not listed but saying he can issue said document is fake.
MCA approved Physicians
However, yachts that are flying other red ensigns, e.g. Cayman Islands also approve the national seamans medical certificate, but it has to be in English and state whether fit for work or not as well as being as per the ILO standards for Seaman's medical examinations.
More can be read at the Merchant shipping notice no 1797,
MSN 1797 (A)
Furthermore, as per MCA following countries seamens medical certificates are considered equivalent to ENG1:
COUNTRIES WHOSE MEDICAL CERTIFICATES ARE ACCEPTED AS EQUIVALENT TO THE UK MEDICAL CERTIFICATE
1 February 2009
This list updates Annex A of Merchant Shipping Notice MSN 1765. To obtain an equivalent medical certificate you must approach the respective maritime authority to be advised of the location of their approved doctors.
This list reflects new Regulations, which came into effect on the 1 September 2002. Medical certificates issued by countries previously recognised as equivalent (listed in MSN 1746 (M+F)) will be acceptable until the date of expiry.
Further countries will be added to this list as and when medical standards and systems have been assessed for equivalency.
Republic of Ireland*
* EU Member States
** EU (European Economic Area) States
Link to MCA website
Code of Safe Working Practices for Merchant Seamen: Amendment 04
Merchant Shipping Notices, Marine Guidance Notes and Marine Information Notes: Consolidated to April 2001