Having been on three marches through the park so far, I am sorely tempted to travel from Derbyshire. It does need to be a focussed protest though, with a clear idea of objectives. If the aim is to get coverage in Thailand, then think about what coverage in the UK there is for demonstrations outside British embassies worldwide. I suspect that the things that will get covered, like the burning of effigies or whatever, will result in people being moved on by the police pretty quickly. I know people will say, well what's your idea then..... and I haven't come up with much more so far than a headless blue and white striped elephant and a banner reading ' 158 years of history, 10 years of incompetence'. Any Wednesdayites in Thailand can really help here with a better understanding of Thai culture.
Of course, if the aim is UK coverage, then it's much simpler.