Most continental campsites have hook-up points that will accept our blue three-pin plugs but it's worth taking a two-pin continental adaptor, in case...
Reverse polarity is quite common abroad where it is not really a safety issue because continental switches cut the power on both the live and neutral wires. In the UK it is usually just the live that is disconnected. So, if the polarity is reversed, an appliance can remain live when switched off. This is only a problem if you touch an exposed part within the appliance, such as an element in a toaster, but it's a situation that's best avoided.
A cheap plug-in neon tester can check for reverse polarity. Simply fix the problem by making up a clearly marked adapter with the live and neutral cables swapped. Alternatively, if connected via a two-pin continental plug, it may be possible to turn the plug upside down.
You may encounter low voltage, leading to reduced performance of appliances. Mainland Western Europe has an electricity supply nominally rated at 220V whereas the UK uses 240V. To cope with this difference, appliances for Western Europe are designed to run at 230V.