It sounds to me from your post that the problem is about lack of credit.
This does not mean that you should go out and get loans and things but to cover all bases for your credit.
Being on the electoral roll is key for gaining initial credit as it shows your address not just now but going back and it gives credit providers an reassurance that if you didn't pay your bills they could find you. It also helps if you do not change address every 5 minutes as lenders would be concerned about tracking you down if you didn't pay and people who change addresses regularly are far more likely to skip payments.
Just being on the electoral roll will not give you access to credit, the lender would want to see a constant record of address and not just that you are now on the roll, it will take time for it to help you but in the end it will give you your biggest boost as far as lenders are concerned.
Getting a store card or a high interest credit card would help too. The pass score for gaining one of these cards is considerably lower than a banks credit card and so this could be a route. A store card will likely charge you interest from day one where as even the high interest rate cards will give you 30 days interest free to repay the debt you run up.
The absolute key thing that you need to do what ever type of credit you take is ensure you make the repayments on the debt and clear the balance in full