Tigermad,
I would suggest that ask the installer to show you his G3 qualification and also who his certifying body is. If he cannot provide it, you should ask for your money back in full. To add a little pressure consider referring him / her to Your local Trading Standards Office - they generally take action in such cases, because they are black and white so easy to progress to a warning letter or for Court action - he / she is either qualified or not.
I would very much doubt that the individual who installed this is qualified. There are far too many basic errors - even the pipe insulation looks like a good attempt by a 9 year old!
Beyond the G3 pressure regulation contraventions, The support fir the base of the tank is in contravention of the Building Regulations - also bear in mind that a tank loading of circa 250kg supported by ceiling joists, rather than floor