Persevere with the new job m8, a couple of lads I know have left and started (with the same company as you) and where a bit unsure at first but now love it!
Don't forget your old employers are about to be taken over by another company, you cant be sure what will happen in the future.
Stick with the new job and if you still dont like it then just keep an eye out for something else, dont forget theres a shortage of operators and new plants being planned to be built in the future (a big new bio ethanol plant has just been announce for Teesside).
Cant you get a transfer from offshore to one of their plants at seal sands?

All the best whatever you decide m8
Steve