Free Traffic Legal Advice

My other half has been suffering from mental health problems, and as such hasn't been opening their post. I opened one of their letters today and it was from Walsall Magistrates Court with the result of a case brought by the DVLA, to "keep a vehicle without a valid licence". I went through the stack of unopened letters and sure enough found a notice of a fine and then one for a Single Justice Procedure Notice.

The first letter was a "Penalty for untaxed vehicle", and was for £636 as an out of court settlement. It's not clear from the letter if this is simply a penalty or includes the back duty as well.

The second letter was a "Single Justice Procedure Notice, which states that if guilty there will be £85 costs and £403.34 back duty added. It does not make mention of the £636.

The final letter was the "Result of court case". which included the above £85 costs and £403.34 back duty, but also an "Excise Penalty" of £660.

Did the settlement figure in first letter include both the back-tax and the penalty?

I'm aware that a statutory declaration can be made, and a guilty plea can then be entered, but will that reduce any of the costs or is it now too late?

Are there any other consequences to this court case, is it a conviction that will affect credit scores or need to be declared in any job interviews for example?

Any advice or help will be greatly appreciated, trying to handle this for them while they get the treatment they need.