Britain's Jewish communities are changing.

Spread the length and breadth of the nation, from Aberdeen to Exeter, they range from small shtibl-style gatherings to 2,000-member synagogues.

But while many of us have a general understanding of where our largest communities can be found - in north-west London, Stamford Hill and Manchester - and an impression of which communities are struggling - the provinces, Scotland, and the north of England - there are some surprises to be uncovered when studying our demographics.

Significant lifestyle changes in the past 20 years, for Jews and non-Jews alike, have affected almost every Jewish community in the country. While some find themselves in terminal decline, others are booming.

Community size is a key factor in almost every aspect of Jewish life - how we pray, how we care for the elderly, how we educate our children, how we keep kosher. We will analyse each of these issues in our State of the Nation series but it is, simply, our numbers in any given location which lay the groundwork for everything else.

Some places are in terminal decline

The hard facts and figures prove much of what people may already suspect. The Board of Deputies' most recent synagogue membership numbers show the fastest growing communities are on the outskirts of London, in Hertsmere - Borehamwood, Elstree, Radlett and Shenley are all thriving. So, too, are strictly Orthodox communities in Stamford Hill, east London, and Broughton Park, Salford.

Meanwhile, dozens of communities in Scotland and the north of England continue to dwindle. Glasgow, Newcastle and Liverpool have all witnessed significant decline since 1990.

In some cases, this can be attributed to the general "brain-drain" caused by graduates and young professionals flocking to London. The capital has long been seen to present better options for young Jews looking for jobs and social opportunities.

Counterbalancing that to some degree is the number of Jewish students who prop up communities around the country, assist with services, volunteer and organise events (see panel).

It is clear, though, that many communities are facing substantial challenges to stay afloat.

Glasgow's two largest congregations - Newton Mearns and Giffnock and Newlands - are considering a merger to share resources and co-operate more closely.

Two other synagogues in the city have closed in the past decade.

While Newton Mearns and Giffnock collectively have around 1,300 members, executives at both shuls acknowledge that a plan needs to be developed now to secure Jewish life in the city, with the ambition being a move to a single building at some point in the future.

Hull Hebrew Congregation was forced to make its full-time rabbi redundant last year because the significant decline in membership numbers left a shortfall in funds.

Harrow and Wembley Progressive Synagogue began a "shul-sharing" arrangement with the Reform Middlesex New Synagogue last summer after selling its own premises to a Sri Lankan Pentecostal church.

But there are many reasons to remain positive about Jewish life in Britain and the continuity of our communities. Even in areas where some might think no Jews live - places such as Chester, Gloucester, Wycombe, Newport, Ipswich and Suffolk for example - small communities and synagogues function, albeit often on a limited scale, but with pride and passion.

Oxford Jewish Congregation provides a unique example of a possible solution to many communities' problem - resources.

Around 300 Orthodox, Masorti and Progressive families in the city share one community centre, which hosts weekly services under one roof, with minyanim of different persuasions often davening at the same time in different parts of the building.

Many communities face problems with their facilities and resources for a different reason: because they are growing so fast.

Radlett Synagogue is looking to rebuild, refurbish and expand its premises and has received planning permission from the local council for a £1.75 million project.

In October, synagogue chairman Andy Katz told the congregation it had for too long accepted "inappropriate and inadequate facilities to pray, to meet, to learn and to socialise". When work is finished, Radlett will have its first, purpose-built Jewish community facilities.

Construction began shortly before last Rosh Hashanah on a new £2.5 million complex for Manchester's Shaare Hayim Sephardi community, providing modern amenities for a merged community which has soared to number around 600 families.

Hendon United Synagogue underwent extensive refurbishment last year to allow its different minyanim to each enjoy substantial space. Its alternative minyan, RCAM, is made up largely of families and young professionals and is larger than the stand-alone communities in many big cities.

Daniel Vulkan, research officer at the Board of Deputies, believes the changes in communities can be attributed to a range of factors and should not be simplified to a north versus south equation, or blamed entirely on London.

He said: "Take Brent in north-west London - there was a very large community, but now it's an area where Jews don't live. It's not affordable for younger people so the remaining community is generally an ageing one, and thus naturally in decline."

Indeed Brent, next door to Britain's most populous Jewish borough, Barnet, has lost half its synagogue members in the past 20 years - a more substantial decline than in most communities outside London.

Mr Vulkan pointed out that some towns and cities were bucking the trend and coping better than may be imagined.

He explained: "You might think Brighton would be declining more rapidly because it is an older community but it's being reinforced by people moving there when they retire. It is the same in Bournemouth and Southend to a degree. This means they are declining, but not as fast as people think."

The release of the 2011 Census results later this year is likely to reveal just how substantial the changes in the community have been over the past decade.