Is it worth trying some injector cleaner first ?

Anyone?

No, it is not worth it IMHO.
It sounds like a cold start issue, which is directly related to a lack of heat in the combustion chamber at start up, giving poor combustion until the heat builds up a few seconds later.

Get the glow plugs checked/replaced.

Regards
Ben (GONE) FL2 2008 SE (manual) Santorini Black, the expensive one
(LEFT WITH) 300tdi Defender 90 the cold, reliable & sensible one

Ben is 100% right
Don't procrastinate, just do it, the glows only cost about £8.00 each.
Kind regards from Fred 2010GS Auto ex Celeb, Santorini Black, 2011 facelift , spoiler, spats, mudflaps, LED footwell lamps, Witter detach,
Other cars:-
1958 & 1959 Austin J40 Pedal Cars under restoration (I make many J40 parts)
If you have an Austin J40 or Pathfinder Pedal Car looking for a new home pls PM me.
2009 Meriva