Christ, really.......
What is the issue with water quality to warrant all these filters?
The pressure drop across the filters should have been looked at prior to installation & also the pre install pressure & flows should have been evaluated as well.
As the filter blocks up the flow reduces thus giving you an indication of reqmt for change or can be done annually maybe if water quality is good enough.
Maybe as the irish would say for the filters - "to be sure, to be sure, to be sure"..................
I would say you are in the UK by looking at the emergency number on the gas meter so surely the x3 water filters are not needed.
Also mentioned as above the gas meter ECV falls to on.
WRONG WAY... Should fall to off for safety. (Clock face - 3 o'clock or 9 o'clock position as you look at the handle - not 6 o'clock or 12 o'clock position).
Your pipework is a right mishmash.
As all have mentioned above - Stopcock (sizing - why not replaced at time of work), isolation valve (is it full bore - why not have a full bore lever valve - a lot easier to use & good flow - no restriction) & then the compression adaptor reducer taking it from 22mm to 15mm & then up to 3/4" maybe - pic not great).
You need to do what other guys have advised above and then i would suggest a re-think of filters & pipework to get the most out of what the water supplier can deliver.
Hope this helps you out,
Thanks,
Andy