His excitement and drive are infectious, and they need to be. However, MacArthur is no stranger to controversy and he has used innovative and sometimes hard-hitting ways to get people to engage with issues relating to young people. In his prev-ious role at Barnardo's he was responsible for a series of shocking ads intended to illustrate the problems faced in later life by children born into acute poverty.
At the NSPCC, marketing activity is split between campaigns targeting adults to raise funds, and cutting-edge activity to drive awareness of its services among children. MacArthur, who is grown-up enough to have two young children, but still rides his BMX in skate parks, is well equipped to embrace this dichotomy.
In conjunction with its Child's Voice appeal, which aims to raise £50m over three years, the NSPCC is expanding ChildLine. The free 24-hour counselling service will relaunch on 19 October and the 35-year-old MacArthur has been working on a marketing campaign to promote it.
He talks proudly about the way that ChildLine has developed, referring in particular to its online offering, which 'now includes one-to-one sessions, message boards, discreet mail, SMS and MMS'.
The launch drive is intended to be a conversation-starter between the charity and young people. 'The proposition is that whatever the problem is, it's better out than in,' he says. '[ChildLine] needs to be in the fabric of all children's lives so that they know they have someone to turn to.'
The work will kick off next week with seeding activity intended to get child-ren to talk online about how they are feeling. Once this is under way, the second stage of the campaign will roll out. This involves partnerships with Stardoll, a virtual fashion game site, Microsoft's instant messaging service and social networking site Habbo.
Children will be encouraged to create videos and soundtracks about their moods, and enter these into a competition. The winners will be collated and turned into a 30-second 'beat-box-style' TV ad by Saatchi & Saatchi, which will break in January.
The project is an ambitious one, but it was not dreamed up by MacArthur or his ad agencies - not the grown-up ones, anyway. The inspiration came, instead, from Idea, a virtual ad agency 'employing' 50,000 young people, which was set up by the NSPCC last December. Briefs issued to the volunteer staff members included coming up with ideas for Channel 4's online magazine show Headspace and the launch of ChildLine online.
'The story that we planned from the start was to put the children in complete control, which is important because ChildLine is about handing control back to them,' says MacArthur. 'It's really important that all our marketing and communications consistently serve up that message.'
MacArthur can, however, claim credit for coming up with the concept for the Idea agency. Rob Lawrence, executive creative director at the NSPCC's digital agency, Razorfish, recalls being baffled by the proposition at first. 'It is very rare to work with a client who is one step ahead of you in their digital thinking,' he says. 'Mac-Arthur is a true creative; adventurous, risk-taking and with exacting standards.'
The Chigwell-born marketer was also behind ChildLine's strategy for targeting an older, harder-to-reach teenage audience, especially boys, which resulted in a tie-up with interactive series Dubplate Drama. Broadcast on Channel 4 and MTV over two years, it allowed viewers to vote on how the plot unfolded. The tie involved ChildLine-branded bumpers and online activity aligning the service with issues such as bullying, drugs, depression and pregnancy.
MacArthur sets great store by the benefits of associating with this type of content, and talks about how NSPCC-backed, but unbranded, TV shows and movies could benefit the charity in future. 'It doesn't have to have a badge on it,' he says. 'Such activity could offer an opportunity for the NSPCC to align itself with relevant issues and create content and conversations around that.'
Assessing the effectiveness of this work could be difficult, but MacArthur displays the relaxed attitude typical of many creatives toward traditional measurement tools. 'It is about getting people to think about the message and, at some level, align what the NSPCC does with that,' he says. 'At what level I am not sure that I mind. It's about brand uplift and brand equity. Where we can measure it, brilliant, where we can't, we can't, and that's OK.'
Whether this will wash with the recently appointed NSPCC chief executive Andrew Flannigan remains to be seen. Before the former Scottish Media Group boss joined the charity in January, questions were being raised about the effectiveness of its Full Stop campaign - the predecessor to the Child's Voice appeal - in bringing down child abuse statistics.
Flannigan was brought in to implement significant change, and MacArthur is imp-ressed by the former media man's vision. 'His impact on the organisation has been really positive, taking us on a new journey and helping us to focus.'
The appointment of the RNIB's Paul Amadi to take over as the NSPCC's director of fundraising from next January is another important change, and MacArthur say he is 'looking forward to seeing what transpires, in terms of his links with marketing'.
Keeping up with the latest digital technology and staying down with the kids, are the two biggest challenges MacArthur faces. By his own reckoning, NSPCC marketing is working. 'Contagious magazine wrote about the Idea agency: "If only commercial brands were clever enough to be doing this",' he says. 'A lot of people don't realise how out-there we are in some of our stuff.'
MacArthur has his work cut out, though. Not only is he overseeing the ChildLine relaunch campaign, but he is also in charge of all ongoing marketing activity, much of which is now tailored to responding to events in the wider world as they happen - another innovative tactic.
He also nurtures the ambition to join the NSPCC's board of directors. 'I think all companies should have a creative on their board,' he says. 'It just changes the way businesses think about things.'
Combine all this with the secret project he cannot talk about, and MacArthur undoubtedly has a busy few months ahead.
This article was first published on marketingmagazine.co.uk