The Observer This is London

The observer herself is being carefully observed in Matt Charman's interesting and, it would seem, well-researched new play set in a fictitious former colony in West Africa as preparations are made for its first democratic elections.

The incumbent president is expected to romp home with a resounding victory, but the initial results prove inconclusive and Fiona, deputy chief of the international observation team, becomes aware that by extending the polling hours – and thereby enabling more of the rural population to cast their votes – a change of government might become a possibility. But herposition is meant to be completely impartial, and Charman raises important questions of whether intervention – with the best intentions and the most fairminded of motives – is permissible or even in the best interests of those it is meant to benefit.

Anna Chancellor gives a fine, determined performance as the hardworking and dedicated Fiona, and is well supported by, amongst others, Chuk Iwuji's local translator, Lloyd Hutchinson's cynical BBC journalist, James Fleet's somewhat seedy Foreign Office civil servant (whose covert reports on her activities include intercepted personal e-mails to her husband), and Cyril Nri in several roles including an intimidating General.

Richard Eyre's fluent and engrossing production makes it clear that what was meant to be a free and fair process has been tainted by offstage violence, and designer Rob Howell incorporates a tension-boosting ticker tape style to monitor the countdown to the final result.

Cottesloe at the National Theatre