London: The traditional “bucket and spade” August bank holiday outing to the seaside is now out of reach for one in five UK families, the Barnardo’s children’s charity warns on Monday.

It calculated the cost of a no-frills day at the seaside for an average family of four could be as much as £170 in some areas and was £41 at the very least.

The research was based the cheapest train fare, using a relevant railcard, for two adults and two children aged between five and 15 from a range of cities and county towns to their nearest coastal resort. It also includes the price of staple items such as sun cream, fish and chips and ice cream.

Barnardo’s found a day trip could cost up to £172 from Aylesbury to Bournemouth; £127 from Leicester to Skegness; and £96 from London to Margate. The research does not include swimwear, towels, buckets and spades, arm bands or inflatables or extra drinks, snacks and meals.

The UK’s poorest families have too little money to cover basic weekly living costs, let alone a trip to the beach, the research found. Their incomes have declined in recent years, due to what the charity condemns as a “toxic mix” of rising living costs and cuts to working and non-working benefits. Welfare changes have included measures that break the link between benefits and inflation.

One in five families have less than 423 a week coming in, based on the government’s 2011-12 statistics for households below average income.

Barnardo’s said its calculations reveal that a family of four on this income could not afford a seaside trip in any of the popular locations it surveyed. Minimum disposable weekly income for the poorest families is 39.

Barnardo’s chief executive, Javed Khan, said: “Family holidays have a special place in the childhood memory box and every child deserves to have a day out once in a while, no matter what their circumstances. Whatever the weather, a day at the seaside with the family is a day to treasure. It is an opportunity for children to spend a healthy, happy time and experience a British cultural tradition; to play on the beach, splash in the sea and build sandcastles. It is an opportunity every child should enjoy.”

Khan said prime minister David Cameron had put family life at the heart of government and promoted the “staycation”, holidaying with his own family in Cornwall, “yet for hundreds of thousands of families struggling to make ends meet this weekend a trip to the pier is but a pipe dream”.

Barnardo’s is calling on the government to the link between benefits and inflation, it says, while ensuring that low income families can keep more of their earnings as the universal credit system is gradually rolled out.