Does it depend than on his declaration??
Yes, I think so. But if they prove you cheating, for example because you're legally employed in local company for longer than 1/2 a year, then you will have to pay fines. And as inWroclaw pointed out in case of UK they have it easier to control than inside of Schengen.
take all my things with me to Poland will be a huge and expensive operation
You would be surprised how Polish competition drove prices down. I guess that transport from UK to Poland is the cheapest on so long distance out of all other countries. First google results:
whole Van up to 1300kg 4200zł 800GBP
½ Van Do 650kg 2100zł 400GBP
But you better find some opinions about these companies before entrusting them your possession. In Munich where I live I would have to pay min 100GBP(120EUR) for 1/2 of Van for few kms.
Also, it is complicated by the fact the company I work for are not happy about me being "based" in Poland.
And that is an advantage of living in richer country.
I thought food was cheaper in Poland - certainly my experience so far.
Cheap food and all types of pork products are cheaper in Poland. Imported goods, higher quality food, like good cheeses not necessarily. Restaurants are definitely cheaper.
it may be my number 1 reason for moving to Poland
we all have known that
The gentleman works in petrochemicals like me so I can say that the situation of coming to Poland may be very advantageous for him.
Yes, I wanted to mention, that more important than tax free allowance is effective tax rate for given salary. And there are few ways to optimize it in Poland (umowy cywilnoprawne for example)
it's not easy to find landlords who do 2 just months,
he can continue staying in hostels like now or rent through airndb.com