"Within UK airspace, for all stages of flight,
instructions to climb or descend cancel any previous restrictions, unless the restrictions
are reiterated as part of that instruction.
Additionally, for aircraft on a SID, the word ‘now’ is added to climb clearances above the SID profile,
to highlight that the SID vertical profile is no longer applicable."
It says instructions to climb or descend cancel any previous restrictions (in this case, i'm assuming the restriction at 6000ft), then they went on to say "Additionally"....so if ATC omitted the word "NOW", it still means the level restrictions are cancelled if ATC ask to climb level above the restriction? Vague. So what if ATC omit the word "NOW"?
From
Here
"2.2 Pilots flying on a SID in the UK FIRs have been briefed to expect climb instructions that cancel the SID vertical profile to include the word ‘now’.
In the absence of this word being used, for instructions to climb above the SID profile, pilots will request clarification from ATC. In some cases omission of ‘now’ has resulted in a delayed climb, and in at least one instance, a deviation from and then return to the vertical profile of the SID, thus generating an increased safety risk, particularly in congested airspace."
MY conclusion: If they omit out the word NOW, I'm going to clarify.