guidance on improving my credit file

Hopefully this isn't too long and confusing...



I want to purchase my flat on Right to buy... will qualify for up to 75% and property is worth between £150-180,000.



Problem I have are I have checked my credit score with Experian and it is poor (525) points. I have a default notice issued on 12/12/2010.



I also have two delinquent accounts with Natwest one was settled on 26/11/2014 and I have just got the other account down from £5500 to £2200 in the last few months. (I have just sent a F & F letter to the debt management company to see if they will accept £1100 as I feel despite having everything else as satisfactory this is causing me major problems because even though it I on arrangement, Natwest are recording it as status 6 on my credit file so it looks like I am paying nothing and making my credit worse every month :(



Is there anything else I can do? It feels hopeless at the moment??



Am I better off saving a much larger deposit? In order to even be considered for a mortgage?





Thanks in advance :)

guidance on improving my credit file