Exactly. If you 'negotiate' once you are opening the door for many others to want to negotiate, and risk accusations of unfair treatment.
Let's say Apple and Facebook come along wanting to "negotiate" but the UK says no, or offers a worse deal. In the US, Google spends several times more on lobbying the government and donations to PACs (donations to political parties/candidates) than either Apple or Facebook. Let's say the same was true in the UK.
It sure would look to a lot of people like Google bribed the government for the deal in a quid pro quo by making donations to the right political parties/people, or spending money on lobbying (where politicians go once they retire or get voted out, at least in the US) Even if that's not what really happened, the appearance is enough for the accusation to be reported in the press and believed to be true by political opponents and cynical bastards like me.