Speaking at a public meeting, Mr Smith claimed a Labour victory in Eastleigh would 'stop the Government in its tracks', while the Liberal Democrat myth that Labour could not succeed in the South was 'patently not true'.
In parliamentary seats where the Conservatives had a majority of less than 5,000 - those most likely to change hands at the next general election - Labour was the challenger in far more cases in the South than the Liberal Democrats, Mr Smith said.
The general election majority of the late Stephen Milligan, the Tory MP whose death created the Eastleigh vacancy, was 17,702 with the Liberal Democrats in second place.
But echoing a similar attack by John Major at yesterday's Prime Minister's questions, Mr Smith said: '(The Liberal Democrats) say they are in favour of better nursery education, yet the nearest Liberal council to this area, in the Isle of Wight, has one of the worst records in the country when it comes to providing nursery places.'
A Liberal Democrat spokeswoman pointed to a list of changes that had followed the party's by- election victories: the end of Margaret Thatcher (Eastbourne), the end of the poll tax (Ribble Valley), the end of Norman Lamont (Newbury) and pensioners' compensation for VAT on fuel (Christchurch).
She added: 'In modern times Labour has not won a by-election from third place.'
Mr Smith's onslaught against the Liberal Democrats comes well in advance of the contest being called. Latest speculation in Tory circles is that it might be deferred until 9 June, the date of the European Parliament elections, rather than 5 May to coincide with the council elections, so avoiding a double defeat on the same day.Reuse content