This paper uses a SVAR methodology to investigate the effects of public investment on growth, and more specifically, the effects of the introduction of a golden rule. We extend the existing literature by estimating a model of the British economy that takes into account long run factors. This seems necessary when dealing with a multi annual variable like public investment, and its long term effects on public finances through debt accumulation. We find that in such a long run framework investment has significant and permanent positive effects on GDP growth; this result runs counter to most recent literature on the topic, that was limited to a short run specification. We further find, by comparing different subsamples, that the introduction of the golden rule in 1997 strengthened this positive effect of public investment.