Thanks very much and it is as I thought.
Seeds of doubt were planted today upon hearing a conversion in which 2 experienced pilots were telling a less experienced pilot that 'Wilco' is unacceptable once inside controlled airspace and can't be used to reply to an instruction. (Which I thought was weird since Wilco = Will Comply and I don't know how you can comply with something you aren't told to do, but thought I perhaps misunderstood)