The Labour leader said voters could not trust what the Prime Minister says after he failed to tell the truth on taxes, small boats and NHS waiting lists.
In Tuesday's ITV debate, Mr Sunak said "independent Treasury officials" costed Labour's policies that "amount to a £2,000 tax rise for everyone".
But a top official at the department had warned ministers that the figure "should not be presented as having been produced by the civil service".
Labour last night said it showed Mr Sunak was "not just hopeless at his job, but a desperate liar" and claimed he had broken the ministerial code.
As he campaigned in Portsmouth, Hants, Mr Starmer said: "What you saw was a Prime Minister with his back against the wall, desperately trying to defend 14 years of failure, resorting -and it was an insight into his character - to lies. I don't say that lightly."
This story is from the {{IssueName}} edition of {{MagazineName}}.
Start your 7-day Magzter GOLD free trial to access thousands of curated premium stories, and 9,000+ magazines and newspapers.
Already a subscriber ? Sign In
This story is from the {{IssueName}} edition of {{MagazineName}}.
Start your 7-day Magzter GOLD free trial to access thousands of curated premium stories, and 9,000+ magazines and newspapers.
Already a subscriber? Sign In
SAINTS ARE SO GRITTY IN PINK..
Jownes neds back Seagulls VAR denies Archer winner
ALEC'S CHAT HELPED POPE OUT OF STEW
OLLIE POPE revealed a heart to heart with mentor Alec Stewart helped pave the way for his return to form against New Zealand.
Daniel doesn't live in reality..it's a fantasy
Mum's words after spy verdict
Slowthai rape accuser: did not envy pal
A WOMAN who claims she was raped by rapper Slowthai has denied she was jealous he had kissed her friend, a court heard.
Gran's fast Lap
Savvy Siobhan's magical journey to see Santa
Missing boat Brits are scuba teachers
Fears couple have drowned at sea
Thanks given for Bruce
HOLLYWOOD star Bruce Willis enjoys a tender moment with two of his daughters as they spend Thanksgiving together.
E-BIKE HIT & RUN MURDER PROBE
YOUNG mum died after being rammed off an e-bike in what police suspect was a murder.
Putin eyes revenge on Britain
Spy chief warns of reckless sabotage
DERAILED
Alexander made Transport Secretary as Haigh resigns over 2014 fraud conviction