Outgoing UK prime minister Boris Johnson on Sunday warned that the country would face “eye-watering” energy bills and promised his successor would soon announce a “huge package” of financial support for struggling households.

Writing in the Mail on Sunday newspaper, Johnson said that while Russia wanted the UK to “buckle” in the face of surging energy prices, the nation had “enough resilience to get through” and predicted a “golden” future for the country.

The government has already announced a £37bn cost-of-living package, which includes a one-off payment of £650 for those on means tested benefits.

But Tory leadership candidates foreign secretary Liz Truss and former chancellor Rishi Sunak are confronting growing calls from campaigners and opposition parties to outline a clear and costed plan to help households.

After Friday’s announcement by the regulator Ofgem, that the energy price cap would increase by 80 per cent in October, taking bills up to £3,549 for the average user, Johnson promised that more government help was on the way.

“Colossal sums of taxpayers’ money are already committed to helping people pay their bills. That cash is flowing now — and will continue to flow in the months ahead,” he wrote in the Mail. “Next month — whoever takes over from me — the government will announce another huge package of financial support.”

Truss, who has advocated for £30bn in tax reductions, is discussing further decreases to tax bills with her team, according to reports in the Sunday Times and Telegraph newspapers.

The foreign secretary is considering a VAT cut of up to 5 percentage points and cutting income tax by increasing the personal allowance, the threshold at which people begin to pay tax.

Truss’s allies have stressed that any decision on financial support will be finalised after a new leader is announced on September 5. According to recent polling of Tory members by ConservativeHome, she has a 32-point lead on her rival.

The foreign secretary is likely to outline a targeted fiscal event in her first weeks in the role and has already advocated for a range of proposals to ease the pressure on households, including a one-year moratorium on green energy levies.

Johnson, who this week visited Ukraine, has reiterated the importance of strengthening support for the country alongside reducing dependence on hydrocarbons sources from Russia and investing in alternative energy sources.

“With every new wind farm we build offshore, with every new nuclear project we approve, we strengthen our strategic position,” he said.