If you going to fiddle the taxman you have to weigh up what you are fiddling and what will be the cost to you if you are caught.
The basis tax is only 20%, so for every £1000 you fiddle you are only profiting yourself by £200.
You have now made £200 tax free, but where are you going to hide or spend it, if the taxman does a full tax investigation they will seach all of your and your families bank accounts, they will visit your home and they will want to see receipts for all of your home furnishings and cars and holidays.
Unless you are going to kept this £200 in a box and never sprend it, then the chances are the taxman will find it, if you use it.
Now the taxman has found you have fiddled your accounts, what will they do, they are not going to just ask for what you owe back, they are going to "access" what you might have fiddled, I can assure you that this figure will be a lot more than what you have fiddled, they will then pass on fines and back interest.
So at the end of the day this £200, could cost you thousands, and if you cannot pay them they could also send you to prison, so now you can say goodbye to your business, your home, you could be made bankrupt, your chance to get a good paying job will be limited because you now have a criminal record.