You reckon? Because right now the top 1% of earners pay 26% of all income tax, which is about as high as it's ever been. For reference, when Thatcher dropped the top rate down to 60%, they were paying 14%. When Labour were all ditzy and mental in the 70's and it was 83%, the top 1% paid just 11% of all income tax. Corporation tax take has been on a strong upwards trend ever since GO started hacking away at it in 2010 (and it's even stronger if you take away the North Sea Oil's erratic contribution - see
here). Analysis of the effects of the rise in top rate from 40-50% are sketchy because it was only there for a short period of time, but the general concensus is that it raised very little if anything and that the behavioural response was significantly greater than was anticipated by Labour in their analysis before they brought it in. This, as a trend, will only continue as the global workplace and labour markets become more and more mobile (for example, there are 104 billionaires in the UK and 44 of them are from abroad - and it's great that they've chosen to come to the UK, but we can't assume they'll stay, nor that our own, home-grown billionaires will either).
Even on closing loopholes, his advisor chappie seems to think that £20bn of the £120bn he thinks is out there is claimable by the exchequer. Even if we assume he's right, then woop de do, that's our borrowing for ~2 months. What about the other 10?
Basically, I think the problem is that everyone - conservative, labour, green, snp, ukip, whoever - think that the best way to raise greater revenues is to have a strong economy, lots of people working (which simultaneously raises taxes and lowers government spending), businesses thriving, investment going up to make it sustainable etc. Everyone loves this stuff - the glorious cream of capitalism - so it really comes down to "who's going to make the economy do better?" As such, I dunno why Corbyn and his gang of backbench rejects bang the gong about "high worth individuals" and corporations and the like when a) it's incredibly difficult if not impossible to actually squeeze anymore, pips squeaking or no and b) it's a drop in the ocean anyway when the real solution actually has little to do with the specific rates and more to do with the economy at large.