Raising VAT just increases the black market as even more people send false declarations through customs and accept cash in hand jobs. My friend in america sends goods to me with all invoices removed to avoid vat and customs charges to ensure a fair price of imported goods.
VAT is an efficient tax in that it is in a business' interest to become VAT registered in almost all cases (so that you can reclaim/only pay the difference between what you've paid and what you've taken in VAT). This is why you'll find a lot of businesses voluntarily become VAT registered well before they reach the turnover threshold.