I think EU countries should be more interested generating real growth rather than looking around for easy pickings.
In various discussions over Tobin tax (transaction tax) your country, I believe has the only precedent of implementation which led to failure of projected income followed by a decline in other taxes (capital gains) followed by abolishment of the tax. It was a failure for Sweden and would be wherever else implemented unless global.
A punitive tax, directed at clients, on spread betting would almost certainly destroy the revenue received from the tax extracted from the spread betting by reducing or destroying the SB companies through the exodus of clients.
UK tax laws are very strange regarding trading even at DMA level. The authorities are reluctant to allow traders in general to become self employed traders for fear that deductible costs can spiral up to levels whereby large gains are offset. It is much more common for trading profits to be treated as capital gains which constrains costs to the annual allowance.