The cost of living in each country fluctuates depending on where you live. So, you need to consider where are you in the UK and where will you be in Poland. In general, the cost of living is cheaper here, but again, it depends on your particular lifestyle (and hopes/expectations if you move).
In general, local goods/services are a lot cheaper. Imported goods/services can be a similar price, maybe even more expensive (especially if imported from the UK). So, in general, cars, (good) clothes, foreign holidays and various other things will cost about the same. Property prices depend on the location - but, in general, are cheaper. Groceries are generally cheaper, but certain items can be expensive (especially lamb and to some extent beef).
In general, I would say that Poland doesn't necessarily have as many different levels of quality (value, store brand, branded, luxury) as in the UK, with less of a value range (unless it's largely blended with the next level up. But the better quality you buy, the closer it will be to UK prices.
I would say bills are normally much lower - you should be able to compare online, but I'd say they could be 50-60% lower (or more) here.
Ultimately, and this is perhaps crucial in your situation (as you will be earning quite a decent wage), there is a certain amount you need as a "basic" standard of living, both here and the UK. For people on a low to average income in the UK, they could probably get by with half or maybe even a third of the earnings they had in the UK. But as earnings increase in the UK, I think you'll find the cost of living gap between the two countries shrinks (for a comparable way of life).
I suspect you wouldn't be much worse off in Poland on the figures you suggest, and might even be slightly better off - again, it depends on your circumstances/way of life etc.
Just a couple of points to note. Firstly, income tax is due to change next year - you might want to check how that would impact on you. Secondly, in cities most people live in flats. In villages, most people live in houses. If buying a new flat (primary market), you will likely avoid various taxes, but new flats are largely concrete shells, with internal walls, electricity/water, but you normally have to finish everything off. The same is true of some new homes, but people often buy the land themselves and build their own home - this can mean that there are fewer homes for sale than you might expect in the UK (people tend to expect to live in a home for longer, without the view to selling).
Building a home comes with its own challenges - I've not experienced this myself, but you can read about it on these pages. However, as a Brit/foreigner, there are various differences in what permits etc. are required depending on the type of property you buy, plus if you need a mortgage, then you'll likely need to be resident here.
Also, homes won't always be as readily connected to "the grid" as is the case in the UK. This can include sewage, water, electricity, gas, broadband etc., especially if building your own home. And a lot of newer villages (and plenty of older ones, too) don't have great roads (when people build their own homes on their own plots, there isn't necessarily anyone willing to pay to build a road, especially if it's basically only for access to/from a few homes).
