As an owner-driver tramping all week, who pays your night out money and how much 
Hello Rob as an owner driver I dont think you can take night out money out of the business but you can claim back expenses for food parking but you have to show receipts. The silly part is you can book into a hotel and then put the receipt in as expenses
welshman is right.
you can pay an employed driver a night out subsistance but as an owner operator you are not entitled to pay yourself a night out allowance.
save any receipts you get for meals, drinks with meals, parking etc and claim them as expenses.
you can get night out subsistance if you are a limited company and list yourself as an employee earning a wage.
otherwise self employed profit and loss scenario.
What Johnny says is correct but you can also, by prior agreement with the taxman, claim a weekly allowance to cover expenses where you don’t get a receipt, for example food from a small snack bar type place or roadside caravan, showers etc. This would normally be in the region of £20 - £30 a week and you should keep a note of such expenses, petty cash vouchers would do for this.
Night out money, what’s that 
If someone asks me to do a job that I know means a night out I add £25 to the price and then use my business card for expenses 
I must have just got lucky then, I payed myself a tenner a night out for years when I had me own, and it went through the books. I also put the parking tickets I got through as well. In fact, so much stuff went through the books that the accountant asked my missus how we could eat.