Just on this point of the Betting Tax - at the moment tax is based on turnover (I think it's 2%) so for every €100 the bookmaker pays €2 in tax regardless of whether the bet wins or loses. Previously, before the advent of online betting, the customer paid this - I remember when I first started betting a £10 bet would cost £11 as there was a 10% tax. As a customer incentive bookmakers (Paddy Power) started to take that cost themselves and eventually the tax was reduced significantly.
The issue (depending on your point of view it may not be an issue, but as a gambler myself this will be an issue for me) with raising the betting tax is that this will reduce the bookmakers profit margins and this will likely results is worse odds for punters. In France they have an incredibly high betting tax and the argument is that people shouldn't gamble so if they lose more that's better because it will discourage them from gambling!
Another result of this would be people betting into "black markets" for which there is no taxation paid - this is already increasing with the actions of some bookmakers in dealing with certain smarter customers.
Anyway it's a pretty convoluted way of saying just upping the gambling tax isn't quite as simple and might have some knock-on effects and a 3% tax on stakes from a 2% tax on stakes isn't likely to lead to a 50% increase in betting tax revenue.