Investors as a class most certainly lobby the government.
> Government services were privatised in the UK for political reasons.
.. and this politics does not exist in a vacuum. There is a whole mythology about privatisation that is put forward by opaquely-funded think tanks. It has other functions simply than providing assets - it's also an anti-strike measure and a means of avoiding complaints.
Some of these entities fund lobbyists and some don't.
mythology ... opaquely-funded think tanks
I don't know if you are a Marxist, but this is a Marxist way of looking at the world, where each class pursues its collective interest, and funds propaganda to spread a self-justifying mythology.
My comment about think tanks was driven by http://whofundsyou.org/ , really. "Funds propaganda to spread a self-justifying mythology" is definitely something that happens to varying extents by various actors - that's effectively how "super-PACs" work in the US. And privatization has the characteristics of a mythology: it's asserted as a cure-all for problems in public services, and implemented even when extremely unpopular. It relies on creating pseudo-markets, often with only one buyer and tiny number of sellers, and the buyer is not the consumer of the service so the quality gets driven down.