Ed Miliband has told 1,100 Norwood supporters that charities should never be regarded as "a soft touch" for government cuts.
Addressing Norwood's annual dinner on Monday at London's Grosvenor House, which raised £3 million-plus, the Labour leader acknowledged that it had been "a very tough year" for charities heavily reliant on private donors.
Paying "tribute to Norwood and the fantastic work it does", Mr Miliband said it epitomised "the values of the great Jewish community that I've got to know better since I became leader of the opposition".
He felt connected to the charity's ethos as his parents came to Britain as refugees from the Nazis - "saved by the kindness of strangers.
"I don't think I would be here on this stage tonight if it hadn't been for the generosity of Britain - but also the values that my mum and dad taught me.
"Like many families, we didn't talk about what happened to my parents. It was too painful and it hurt too much.
"But having struggled for life itself, they instilled in us a sense of duty to leave the world a better place than we found it. I know that's why so many people are here tonight."
Chief executive Elaine Kerr highlighted the impact of cutbacks in government and local authority support. "Unfortunately, this is not a one-year problem," she said. "We have to find the additional monies year after year." Norwood continued "to seek out efficiencies anywhere we can to reduce costs - but not at the expense of our front-line services."
She further explained that, with advances in medical care, "people with learning disabilities are living longer, too. This creates the need not just for support and care over a long period of time, but also for additional services not required in the past." More children were being assisted, whether as a result of abuse, family break-ups or poverty.
A strategic review would provide clarity "on our medium- and long-term aims and can give parents of young children who will need Norwood for the whole of their lives the reassurance that we shall indeed be here for them."
She also stressed the importance of the new Young Norwood Consultative Committee, which would help to shape the charity's future. Its involvement was crucial to providing "a worthy inheritance for future generations".
Among young supporters at the dinner was Adam Banin, 28, who said: "It's hard not to get involved when you see the work they do. People here are not going to invest unless they see a return."
Israeli ambassador Daniel Taub pointed out that "7,000 people benefit from Norwood's services. It's one of the bright stars of the Jewish community."