You're not reading what I said.
If you pay in full, that's the end of it, no defence, you missed the deadline. If you pay within 30 days you can have the entry removed from your credit record. Otherwise it will be on your record for six years.
If you pay to have the judgment set aside it will cost you >£300 and only if the court accepts this will you be able to submit a defence. You will need to construct an outline defence for this to work.
Feel free to ask for a second opinion if you do not believe me. I have never been in your situation.