This study analyses the effect of firm characteristics and governance mechanisms on cash holdings for a sample of UK SMEs. The results show that UK SMEs with greater cash flow volatility, and institutional investors hold more cash; whereas levered and dividend paying SMEs with non-executive ownership hold less cash. We also find that ownership structure is significant only in explaining the cash holdings for firms with high growth investment opportunities, and leverage is only significant in explaining the cash held by firms with low growth investment opportunities. Our findings suggest that internal governance mechanisms are more effective for SMEs with high growth investment opportunities, while external governance mechanisms, such as capital market monitoring, are more effective for firms with low growth investment opportunities.