Abstract For the design of sea defences the main statistical issue is to estimate quantiles of the distribution of annual maximum sea levels for all coastal sites. Traditional procedures independently analyse data from each individual site; thus known spatial properties of the meteorological and astronomical tidal components of sea level are not exploited. By spatial modelling of the marginal behaviour and inter-site dependence of sea level annual maxima around the British coast we are able to examine risk assessment for coastlines and the issue of sensitivity to climatic change.