He didn't 'get off' with anything. That assumes that he was guilty and has somehow managed to hoodwink the court.
He was found 'not guilty'.
His defence that he is functionally illiterate was to illustrate that any attempt to mastermind an elaborate fraud would have been beyond his abilities.
Being illiterate does not mean that he is not able to do his job very well indeed. His present and past successes are testament to that.
HMRC were not able to press their case that he is a crook and has 'stolen from the public purse'.
The newspapers have fudged this a bit.
He wasn't charged with c.£190,000 worth of tax evasion....he was charged with evading tax 'on' £190,000. Quite a difference.
I assume that he claimed the money in question was either a) not liable to tax in the first place, or b) was the balance of a larger figure on which he 'had' paid tax.