OK, like you say, you can't see all from the photos. The arrow on the tf1 is indeed pointing upwards but the return pipe connected to the upper port is flowing downwards from a downwards return pipe from behind the boiler. The lower port bends upwards to the return tail of boiler.Obviously we cant see everything from the photos but nothing immediately concerns me with those photos, obviously I can't see how the tiles are fixed but I can't see the gap you mention. The filter looks Ok but again I can't see which way the direction arrow is pointing, if it's pointing up then all is good. So the only concerning parts is the benchmark not filled it, the flue not been clipped and the possibility he hasn't commissioned the boiler, and the condensate looks like it might be running slighlty up hill. If you are generally concerned then you can either call gas safe or another local engineer to come and check it over.
The flue is way off vertical for starters, is not held to any structure in the roof by any clamp or brackets, it's only held by its own downwards weight and a loose fitting collar of the lead slate. The roof slates are layered loosely behind the upwards section of the flue.
The condensate pipework is forced behind the filter pipework. There's an adey calmag cold supply filter tightly fitted between other pipes running downwards and is dripping but no space to get wrench on it to tighten up. Out of shot are also 2 crossovers that are not freely crossing, they are forced against the pipes they're crossing over. The mains supply cable has been scarred with heat from the torch, as has a few areas of the boiler under tray.
I could go on..... Yes, I'm fussy but there are several areas that are clearly and unnecessarily bodged.
Having watched the guy work, I don't believe he has the skills or finesse to put this right to a satisfactory standard so I can't see any sense in confronting him with a view to putting it right.
I'm screwed I reckon..