New book poses the question -- Just how English are the English? The English World: History, Character and People, edited by Robert Blake. New York: Harry N. Abrams. 268 pp. $50.

Who are the English and how English are they? These are key questions considered by a galactical team of British scholars in this coffeetable book, lavishly produced with an eye to the nostalgic reader. In his introduction Lord (Robert) Blake, provost of the Queen's College at Oxford University, emphasizes how England ''developed on different lines from the rest of Europe,'' how the original wealth based on wool, the Reformation, and ''social fluidity,'' allowing a class but no caste system, with long periods of peace, all combined to produce a world power so puzzling to foreign observers.

The English, explains Frank Barlow, were a racial mixture, ''mongrels'' from earliest times, and the Norman invasion introduced further confusion: ''it is not easy to decide at what point after 1066 one can speak of English nationality or patriotism.'' Moreover, ''distinctive national characteristics were not prominent in high medieval England,'' explains George Holmes.

Yet institutions evolved, monarchical (described by Michael Maclagan) and parliamentary (examined by Blake), in a United Kingdom of fragile unity, mainly because of Ireland (considered by Hugh Trevor-Roper), and which forged two world empires (analyzed by Herbert Nicholas and Max Beloff, respectively).

Ultimately the Second British Empire owed allegiance to Queen Victoria, the ''Grandmother of Europe,'' a half-German married to a wholly German Prince Albert, the present Queen's great-great-grandparents. How English are the English?

The answer to this question is to be found, paradoxically, in ''the English diaspora.'' How could such a seemingly insular people expand so vigorously and successfully? Children at the ''teddy bear age'' were trained at public schools in leadership; politicians emerged from the ''Mother of Parliaments''; all were nurtured on English, ''a mixture of many different languages'' (Kenneth Muir) which included Shakespeare; many belonged to a church based on compromise and a Bible as memorable as the King James I Authorized Version - ''the greatest spiritual treasure the English church has given to the world'' (Edward Norman).

The debacle of the First British Empire in the New World instilled the wisdom necessary for the running of the Second British Empire in India, Africa, and Australia. The American connection is repeatedly referred to in this book. Nothing ever stopped or inhibited expansion: not the French Revolution, nor the Spanish Inquisition. Even the blemishes, such as appalling post-Industrial Revolution conditions and an inhuman criminal code for the underprivileged, encouraged, indeed, prescribed emigration. At the same time, as Quentin Bell cogently argues, ''the English Spirit'' was artistically, above all architecturally, fully receptive to European influence.

As for the real Englishness of England at village level, Richard Muir enthrallingly evokes history behind many a hedgerow in a landscape now sadly ''threatened by the visual sterility of modern farming practices.'' Sydney Checkland's consideration of England as ''a Nation of Shopkeepers,'' with an economy now suffering from ''stagflation,'' and Asa Briggs's tour de force on English custom and character, based on a collection of intriguing quotations, conclude the book.

The illustrations are particularly interesting, especially the social juxtapositions: pictures of the upper-class National Liberal Club and the working-class Bradford City Band Club; a very superior Eton schoolboy watched by three poor and incredulous East Enders; also an overcrowded Brighton beach and ''the select few'' at a Buckingham Palace tea party preserving a respectful distance from Her Majesty.

Although Lord Blake echoes fear of ''Parliament becoming an elective dictatorship'' and the wish for a Bill of Rights, it's largely a cozy, nostalgic , and beautiful ''English World'' which is presented here, significantly omitting such unmentionables as the Toxteth and Brixton riots or the present disquiet about the police. The trouble is: Today's English World is no longer truly English!