Sarah Sands: See why diversity works – switch on your set

It has been a rough year for the BBC, but its programmes have never been better. It ends the year with two dramas of towering intent and execution.

Tonight is the first part of Small Island, adapted from the Andrea Levy novel. For Christmas, hurrah, we have the second series of Cranford. If the BBC had lost its grip on period drama it would have deserved the fury of its critics. But we have Judi Dench back in her bonnet and can rest easy in our beds. Small Island is also first-class drama with first-class acting.

When Greg Dyke called the BBC "hideously white" he spread a panic about the lack of ethnic diversity. But one should be realistic about representation. Jane Austen was just not very diversity minded. It would have been a pity, as well as a commercial disaster, if the BBC had ditched Austen as a result.

Dyke was also unobservant about the different geographical demographics of Britain. I remember a lunch with a television big cheese and the Telegraph columnist and BBC licence martyr Charles Moore. The television chief talked of the scandalous lack of ethnicity on screen, relative to the British population. I nodded furiously, citing my experience of London. Charles politely pointed out that television was not underrepresenting the ethnic population of Sussex.

Race on television has not been an issue this year, which makes the superb production of Small Island all the more potent. From nowhere, comes a drama of such humanity and comedy that it is life enriching. Coincidentally, it is being shown days after the all-black cast of Cat on a Hot Tin Roof won such praise from theatre critics. The cast members were not simply black, they were exhilarating.

You will not see much finer acting on television this year than from Naomie Harris, playing Hortense in Small Island, the haughty, vulnerable young Jamaican wife, or from David Oyelowo, her striving husband, Gilbert, or from the white actress Ruth Wilson, as Queenie the landlady at the emotional heart of the drama that illuminates a period of British history, the post-war Windrush immigration from the Caribbean. Despite the crude racism – "no niggers, no dogs, no Irish" – in its way it was an age of migration innocence. The newcomers carried British passports, pledged allegiance to the Queen, respected English history and language. Hortense and Gilbert talk always of the Mother Country. The prejudice they encounter is fear of the unfamiliar, rather than anything more organised.

What makes it such compelling television is the personal rather than social relationships. Hortense is cold and affected at the start, until she finds that her proudly held teaching qualification count for nothing in Britain. Her exasperated husband nevertheless finds her touching and is grateful for the unexpected tenderness that she eventually shows. Queenie tests the limits of society by her love affair with a Jamaican. It is a tough and tragic tale but fellow feeling and human dignity prevail. The story of racial integration is essentially optimistic.

Each new wave of immigration brings social tensions and anxiety. And what of those who do not love the Mother Country, but despise it? Yet the many who arrive here, work hard, prosper, settle. Queenie understands the drabness of Britain without immigration and grabs her chance of excitement, defiant of the heart-breaking consequences. The real point of diversity, on television and in life, is not that is correct but that it is vibrant.

Sarah Sands is deputy editor of the London Evening Standard