MPs have voted the RNID and Macmillan Cancer Relief the most effective campaigners out of 13 charities in a survey by the Future Foundation.
Last year, the RNID's supporters sent 50,000 postcards to MPs asking for digital hearing aids to be provided free. At Christmas, the Government announced an extra £20 million for the scheme.
An RNID spokeswoman said: "I think MPs were taken aback by the number of responses they received from our supporters."
Macmillan held a reception to lobby MPs about the £1 million annual VAT bill it faces on the refurbishment of NHS buildings. The charity hopes this month's Budget will remove the tax.
The Future Foundation questions 250 MPs every six months about the effectiveness of campaigns by charities, including Guide Dogs, Barnardo's and the National Trust. In the last poll, carried out in summer 2001, the NSPCC's Full Stop campaign had made the most impact with MPs.