Listening to the Rest is Politics this morning, apparently Labour have never actually promised to increase overall spending and will in fact cut it. I think people expect them to spend high because they are Labour but they have been quite cautious in what they have committed to. They have also made the pledges not to increase taxes on working people or VAT, corporation tax etc so have tied their hands somewhat because these are by far the biggest revenue raisers.
Labour actually played quite a clever game in the campaign where they put a lot of focus on gimmicky or niche policies like VAT on school fees, ticket touts etc. I think they intentionally avoided too much talk about the big stuff like how they would fix the NHS or achieve economic growth.
The tax policies they do have are highly unpredictable in terms of the revenue they might raise - non-doms can mostly leave the country if they want to; if you increase capital gains tax people will probably hold onto their assets; VAT on school fees might raise a bit of revenue but it's very hard to predict how the education market will respond.
I do think increasing resource to HMRC is a good idea - HMRC have had their budgets cut and they simply can't enforce all the anti-avoidance law available to them. They are also hugely disadvantaged by paying a fraction of what the private sector pays to their staff for the same skillset. I've known HMRC to lose multi-million pound cases by not filing documents in time.
I think the scale of large corporations avoiding tax is overestimated and very few such corporations are actually evading tax. It's not easy to get facebook et al. to pay their "fair share" of tax in the UK partly because other countries have a different idea of what their "fair share" is and you can't (usually) tax the same profits twice in different jurisdictions. We actually do have law to try to achieve this already though - our tax system is very advanced in this respect in international terms.
The ideal is obviously to fund spending through growth in the economy but that takes time and is easier said than done. And you're not likely to attract many businesses here with 40% capital gains tax rates.