The Labour Party, and interestingly it is the party rather than the government or 10 Downing Street are inviting anyone "tell us what you want to say to the G20 world leaders before the summit and we’ll make sure we pass on as many of your comments as possible". The site asks for a question in no more than 200 words (though they state the optimum is 140 characters) and an email address, and this is the one bit that draws suspicion, they warn that "The Labour Party and its elected representatives may contact you using the data you supply". So clearly it is a device to collect emails and can be used for promotion, which is essentially a core rule of campaigning so understandable, and any contact from visitors may suggest wanting to start a conversation anyway. But the question is how many of the questions actually will be answered. You are able to view the questions, but there is nothing to say if these questions will be posed, how, or how any feedback will be given to those asking the question. An interesting idea though and gives the impression of listening to the 'market', however as with many of these things it requires some follow up to make people feel their views matter.
Just as an afterthought, whoever designed the picture did not think it through too well. Obama looks straight at the visitor smiling, this conveys the image of honesty and openness as well as him as a likeable person. Brown is staring into the distance looking serious but also slightly aloof (my impression) but it does kind of set them as being very different when Brown may well want a little of Obama's charisma to rub off on him. Perhaps it is intentional and serious Brown is felt to be the better image to convey but I wonder if the juxtapositioning of the two contrasting images is wise.