Covid-19 levels are continuing to rise in all four countries of the UK, with the increase fuelled by the Omicron variants BA.4 and BA.5, experts have said.

Figures from the Office for National Statistics (ONS), based on swabs collected from randomly selected households, reveal that in the week ending 18 June an estimated one in 40 people in the community in England are thought to have had Covid – around 1.36 million people – up from one in 50, or 1.13 million people, the week before.

The estimated number of people testing positive for Covid also rose in Scotland and Northern Ireland in the most recent week and, to a lesser extent in Wales, with levels highest in Scotland where around one in 20 people, or 4.76% of the population, are thought to have had Covid in the week ending 17 June.

“Rates have continued to rise across the UK, with the largest increase seen in Scotland,” said Kara Steel, senior statistician for the Covid-19 Infection Survey.

“In England, infections increased across all age groups, with the lowest level of infection seen in school-aged children. These increases are largely driven by the Omicron BA.4 and BA.5 variants.”

According to the latest ONS data, infection levels have risen across all regions of England, except the north-east and the south-east, where the trend was uncertain, and across all age groups.

Levels are currently highest in London, and among those aged 25 to 34 – with around 3.3% of the latter estimated to have had Covid in the most recent week.

Overall, it is estimated 1.7 million people in private households across the UK had the virus last week – the highest figure since the end of April.

Experts have previously said the rising level of infections is likely to be down to a number of factors including waning immunity, a return to pre-pandemic behaviours and, in particular, growth of the BA.4 and BA.5 Omicron subvariants, which have been deemed “variants of concern” by the UK Health Security Agency (UKHSA).

Research released earlier this month revealed that an Omicron infection offers little extra protection against catching it again, while on Friday the UKHSA said BA.5 was growing 35.1% faster than the previously dominant Omicron subvariant BA.2, while BA.4 is growing approximately 19.1% faster.

“These new variants are overtaking the plateauing or declining older ones in the UK, and similar patterns of rising infections are occurring across Europe,” Prof Adam Kucharski of the London School of Hygiene and Tropical Medicine told the Guardian. “This will be the third wave of a distinct Omicron variant in recent months, after BA.1 and BA.2, and countries are likely to face more in future, so we can’t view Covid as ‘one more wave and then it’s all done’.”

Hospitalisations are also increasing, with data from the UKHSA released on Thursday revealing the hospitalisation rate for Covid in England has risen from 6.11 per 100,000 to 8.20 per 100,000, with rates highest in the north-east and in those aged 85 and over.