Breaks seem quite complex to design into the boat in a way that will both comply with the VAT Notice 744C (which seems to impose more restrictions on breaks than in the Merchant Shipping Acts) and be aesthatically pleasing. But the good news is that the tonnage factor is actually 0.35 - which could make a lot of difference.
What intrigues me is how the restrictions that the revenue are purporting to impose in the current VAT Notice 744C on measuring the deck position on a narrow boat, and excluding height to the cabin roof, fits with the Tribunal decision in Switftcraft Boats (20489, released 30 November 2007) which specifically decided this point.
For reference, the factor is in section 2.12 of VAT Notice 744C:
"2.12 What if my ship has a break in the line of the deck?
A break is a raised portion of the deck that extends from one side of the ship to the other. Cabins, wheelhouses, hatches and erections above the deck are not breaks.
If the ship does have a break, the mean length, breadth and depth should be multiplied together with a factor of 0.35. This resultant figure should then be added to the gross tonnage when calculated using the formula given in paragraph 2.10."