The gas network operators are already discussing subsidies with government for upgrading/modifying the infrastructure. Firstgas indicated that at least 1/3 of their infrastructure would need to be replaced before the introduction of hydrogen at levels greater than 1%. Then there's the cost of modifying customer premises equipment, let alone training, certification etc.
The government are also being asked to subsidise hydrogen refilling stations, and even large trucks. Given the inefficiency of hydrogen generation, storage, and the highly inefficient fuel cells, we will need to produce huge volumes of gas, so the allocation of funds will need to be significant. Consuming vast quantities of water to electrolyse is ironically also likely to be very unpopular amongst environmentalists.
Given these and other issues, I'm just not convinced an accelerated deployment is viable either fiscally or logistically.