He joined the polish army and was a dispatch rider in Italy.
If your grandfather was in the Western Command Polish army, these people will have his records:
APC MS Support - Disclosures 5
West End Road
Tel: 0208 8338603
Fax: 0208 8338866
After the war he lived in England and worked in a coal mine.
I would very much expect that he was in the Polish Resettlement Corps. You can find lots of information about the PRC at this excellent website polishresettlementcampsintheuk.co.uk
He was in a forced labour camp working on a farm before the German invasion.
Sounds like he'd done something to annoy the Polish junta (the Polish government in the years before the war really was very unpleasant, right down to the concentration camp at Bereza Kartuska that some Poles still insist was just a "seclusion camp"), in other words he was most probably a good bloke.
After the invasion he was in a panzer regiment in Africa and was found inside a burning tank.
There were more than a few Poles in the Afrika Korp. According to Col Kuropieska, the post-war military attache at the Polish embassy in London, all of his staff had been chosen from a Polish repatriation camp and all had served in the Afrika Korps. But your grandfather would have been one of the few Poles who changed sides before D-Day (of the 89,000 Poles who served in both German and western command Polish armed forces, only 4,500 joined western command Polish armed forces before D-Day).
Got married and immigrated to Australia in the 60s.
A ten-pound tourist! I wonder when he took British citizenship (his emigration to Australia in that decade very much suggests that he had British nationality when he left UK).
Got to say that there's a lot to like about the sound of your grandfather.