Perhaps you could look for a major swedish or European contractor who has contracts in the UK?
They may be able to see both sides the first that you are qualified except for a piece of paper and they would understand the level you are officially qualified to, so with a little extra money you get to officially finish your apprenticeship and have an income.
My advice is if possible take the £80.00 per week for one year that way you have the papers to travel to any country you wish in the future, without that piece of paper you will always be classed as a laborer / plumbers helper.
They may be able to see both sides the first that you are qualified except for a piece of paper and they would understand the level you are officially qualified to, so with a little extra money you get to officially finish your apprenticeship and have an income.
My advice is if possible take the £80.00 per week for one year that way you have the papers to travel to any country you wish in the future, without that piece of paper you will always be classed as a laborer / plumbers helper.