I can understand why the UK government would sell the seized crypto. It's normal for governments and companies facing financial difficulties to sell assets they don't need. However, this would never solve the problem with the budget deficit. The only measures that would reduce the budget deficit are cutting government spending and raising taxes. I prefer the first option, nobody wants to pay higher taxes and increasing the taxes would hit the economy. The UK was living off of debts for too long. Now, the debts have to be paid.
Governments selling seized BTC might be a good thing for the Bitcoin market. More BTC gets into circulation and the BTC price drops for a while, which presents a great buying opportunity.