We apply a dynamic perspective to forecasting votes and seats in British elections. Our vote model captures the swing of the electoral pendulum between the two major parties while using prime ministerial approval as the (sole) short-run predictor of vote choice. The seat model incorporates the inertia of the previous seat distribution while translating votes into seats. The models forecast the lead of one major party over the other (percentage for votes and number for seats). The statistical estimation includes data on British elections since 1945, although the test for cycles (swing of the electoral pendulum) goes as far back as 1832. The vote model picks the winner of every one of the 1945–2005 elections (out-of-sample forecasts) and is rarely off by more than 2 percentage points. The seat model does almost as well, rarely missing the seat lead by more than 25.