Aren't there ferries from north england to sweden/ estonia? Just a trip across to gdansk then.
Not a sausage, there may be freight ferries (though a quick search says no) - but the nearest thing to a UK-Scandinavia service these days is Harwich-Esbjerg. You'd then have to drive across Denmark and Sweden and then ferry from there to Poland.
There's an interesting alternative in Rostock-Gdynia, but it hardly seems worth it.
These guys suggest via amsterdam
No point, he's in Portsmouth. There's also the Harwich-Hoek van Holland service which might make sense - Portsmouth to Harwich is a straight run, instead of crawling across the south coast.