Jews are being asked to stand up and be counted in next month's Census.
The national population survey, which takes place on March 27, will again include a voluntary question on religion, first introduced 10 years ago.
Now the Board of Deputies is calling on all members of the Jewish community: "Tick the box marked Jewish."
Strictly Orthodox leaders are also encouraging greater participation after an undercount of the Charedi population last time round. Census results are used to calculate funding for housing, health and other social services. They can also help Jewish organisations plan to meet community needs in coming years.
A Board spokesman said: "Knowing how many Jews live in a particular area will make it easier, for example, to allocate financial provision for pupils in Jewish schools and provide care for our elderly, justify the provision of additional Jewish schools and ensure adequate resources are set aside for protecting communal buildings."
Ten years ago the community lost out on valuable funding due to numbers being underestimated. Hackney, which includes Stamford Hill, recorded fewer than 11,000 - half of the strictly Orthodox population living there.
According to the Interlink Foundation, a Charedi charitable advisory service with branches in London and Manchester, many families did not return the form and fewer than 60 per cent answered the religion question.
But in advance of next month's survey, the foundation has published a letter on its website from Rabbi Shimon Winegarten, of the Bridge Lane Beis Hamedrash in Golders Green, to say that filling in the census was a "legal obligation" and there was "nothing in halachah that militates against that."
Interlink director Chaya Spitz said: "We are encouraging people to stand up and be counted."
Charedi representatives have advised local Census officials on how to improve participation, for example by not trying to collect forms at Pesach.
One problem, she said, is "the Census form only has space for six members per household. So if you want to put in more, you have to ask for an additional one."
What may have happened in 2001 is that some strictly Orthodox respondents with large families may have stopped at six, under-representing the size of their household.
This time, she hoped, extra forms would be offered to people. "If you are able to show your true numbers, public bodies are more likely to listen to you."
