> ... not earth shattering

In 2015 the revenue from the UK constituted 15.6% of total EU revenues for that year. It's a significant share.

> ... the tax would go to national governments and not the EU budget.

In 2012 the Commission recommended that two-thirds of the revenues from the FTT should go to the EU budget and the remaining one-third should be retained by the EU Members. It's reasonable to think that at least some portion of this tax will go to the EU budget directly.