Mani20096, no you don't need to pass class 1 again for 14 ATPL exams. Just do your exams there and you will have a certificate for CPL/IR practical so you could go to UK or stay in Poland or choose third country for practical training
If you mean ATPL integrated - you will need FE approved by UK if you wish to have UK licence
About difficulty of exams - I finished mine more than 1 year ago. It was not easy nor very difficult. But I didn't try UK exams so not able to compare
I know that now there are some open answer questions but its not very difficult. And question bank like aviationexam helped me a lot (but it is not perfect QB)