While it's true that legally if you move to the UK, you are not able to drive a non-UK car there, in practice this is not enforced (for people who just moved to the UK - for long term residents it's different and there were some crackdowns on non-UK registered cars that were parked for a long time in the same place in some areas), and it would be really hard to do so anyway, as in the UK there are no residency cards. (The drivers licence acts somewhat as residency card as it shows your address, but you probably don't have a UK one yet). You can read more about it here. So for the first 2-3 months I wouldn't worry, just make sure you can provide your ferry/tunnel ticket that shows when you entered the country.
However after the few months you have to register your car, and you can only do it if you modify it to UK standards. While the position of the wheel is not a problem (people like to import and drive US cars as well, which are LHD as well), you will need to replace the headlights to dim to the left side, and the speedometer to show the speed in miles and not km/h. Also because it will still be a LHD car, it'll be a bit inconvenient to drive it around in the UK, and also the insurance costs will be higher. Selling it will be problematic as well, as most people don't buy LHD cars in the UK. If you want some money out of it you probably need to drive it back to Poland to sell it there and then get back to the UK using other modes of transport.
You might be able to buy a UK registered car abroad, however you need to find a seller - probably someone who just moved back from the UK to Poland. As all paperwork you have to do can be done via post or online, it should be possible for you to do so. However you already need an address in the UK for this to work, as both the insurance companies and DVLA will send you the documents (the V5C certificate) to that address. Also legally you won't be able to drive your car outside the UK without the V5C certificate as well, so someone will need to send them back to Poland to you - I'm not sure if the copy of the V5C the seller gives you would be enough.
If you can't find a seller, or you won't have an address and someone to send back your documents until you move out, then the best thing to do is to hire a moving company to help you with the transport and use public transport (train, coach or plane) to get to the UK. If you are really inclined to drive there you might be able to hire a car from one of the international companies for one-way as well, but the one-way return cost for the hire car would be quite prohibitive (£1000 or more) as well.