Hello I am a solicitor with 20 years experience. I will try to help you with this.
No yo can not do this unless the customer is saying he wants you to take it away. You would be at risk of being prosecuted for criminal damage if you did this. You would also haveto trespass on his land to do it.
How much does he owe you?
If it is less than £10,oo then you can start a claim in the small claims court for the outstanding money. You should first send a letter explaining what he asked you to do , what you did, the price agreed and that you have asked for payment following completion of the work which he has refused with no good reason to do so. You should give him 14 or 21 days to pay the outstanding amount and warn him that if he doesn't then you will take him to court to seek recovery of the money.
Follow this ink for the government website on how to make a money claim. https://www.gov.uk/make-court-claim-for-money/overview
The small claims court is designed to be simple to use and to avoid the use of lawyers with all their associate costs.