Based on his number I assume the he was in the Royal Navy but attached to the Polish Navy due to the sensitivity of his job in communications, and presumably the ability to speak Polish.
As for the award I think you would need to start looking from the Polish end, ie the Polish Government in exile or the post 1945 Polish Government. As for which medal he was awarded, I think the most likely one is the Maritime Medal or the Polish Navy Maritime Medal (
Wikipedia article here in Polish). This was a Polish military decoration established by decree of the President of the Republic of Poland Abroad in London on July 3, 1945. It was awarded to sailors of the Polish Navy for distinguished service and impeccable conduct at sea during World War II. Quoting from the Wikipedia article as translated by Google "It could be awarded for the first time to a sailor who had been actually embarked on Polish ships participating in combat operations, armed vessels incorporated into the Navy, or ships and vessels of allied nations for a period of six months, or for a period of one year on such ships and vessels not permanently engaged in operational and combat conditions. For subsequent awards, this period was one year. The period of service was counted from September 1, 1939. The medal could be awarded four times."
The granting of permission to wear it along with his British medals, though formal in nature, was fairly routine. I can't quote the precise Royal Navy rules from the time but I suspect they were not substantially different to the current rules, as set out in Joint Service Publication (JSP) 761:
Annex A to chapter 10 of JSP 761
RULES GOVERNING THE ACCEPTANCE AND WEAR OF FOREIGN ORDERS, DECORATIONS AND MEDALS BY CITIZENS OF THE UNITED KINGDOM AND HER OVERSEAS TERRITORIES
10A.01. The following are the extant HMG Rules approved by HD Paper and administered by the Foreign and Commonwealth Office who are the responsible authority:
10A.02. These rules set out the circumstances under which a citizen of the United Kingdom or her Overseas Territories (“UK citizen”) may be granted the Sovereign’s permission to accept and wear an Order, Decoration or Medal (“foreign award”) conferred by a Head or Government of a foreign country, Head or Government of a Commonwealth country of which the Sovereign is not Head of State and certain international organisations (collectively referred to as “foreign state”).
Principles
10A.03. No UK citizen23 may accept and wear a foreign award without The Sovereign’s permission. Such permission must be sought as soon as there is an indication that an award may be offered.
10A.04. The granting of permission for a UK citizen to accept an award offered by a foreign state will only be considered if the award recognises specified services rendered to the interests of that foreign state.
10A.05. Permission will not be given for UK citizens to accept a foreign award if they have received, or are expected to receive, a UK award for the same services.
10A.06. Acceptance of a foreign award does not mean that the UK will make a reciprocal offer directly or indirectly associated with the UK recipient.
Permission
10A.07. Permission to wear a foreign award, if granted, will be either:
a. Unrestricted – allowing the award to be worn on any occasion; or
b. Restricted – allowing the award to be worn only on particular occasions associated with the foreign state that conferred it.
10A.08. The grant of permission, whether unrestricted or restricted, will be conveyed by letter to the UK citizen concerned from The Sovereign’s Private Secretary
