I am employed as a bar worker, and I would like to become fully self employed blind fitter.

I have done a couple of jobs in my new field, and have invoiced the customers, (around £2000 worth of work over a year)

I have not kept ANY records of thee invoices, and will not be able to recollect all of the jobs.

I want to register as SELF EMPLOYED but I was wondering if this coud come and bite me in backside in the future, and what I should really do????
From now on keep proper records of everything you do. Speak to your local Business Link for free help and advice on all aspects of becoming self-employed. If you're not setting up a limited company, you don't need anything terribly sophisticated but if you think your business is likely to take off it's better to set up a decent system that will grow with you so that you don't have to redo it when you're busier.

Strictly speaking you should have let Inland Revenue know about your self-employed earnings but, as others have said, it's not likely to cause problems. Just make sure you do it the right way from now on.

Good luck!
All work should be invoiced and a copy of that invoice should be kept. Use a triplicate book that gives carbon copies. Give one copy to the customer, leave one copy in the book and keep the third copy in a filing system at home in case you lose the original book. Any work that you have done should have been declared to the Revenue, however it is unlikely to come to light, especially if the work you did was for private homes - if you have done work for a business or a landlord then they will offset the cost of that work against their tax and there is a very small chance that it could come to light if they were subject to a tax investigation. Just make sure that you keep proper records from now on and also make sure that you keep every scrap of paper regarding your expenses, to allow against your tax.
Don't worry about it. The main thing is from now on, DO keep copies of all invoices!

Whatever you did in the past before registering is just that - in the past.

Once you are registered, like I say, keep track of such things. Even at the simplest, just buy a small multi-pocket folder to put your business bills and copies of invoices in.