That is according to the results of the latest UK Prosperity Index, in which all council areas were assessed on a raft of criteria - and ranked according to how they were performing by those measures a decade ago and how they shape up today.
The borough fell more than 70 places in the prosperity league table, which was devised by the think tank The Legatum Institute.
Chorley has also lost its crown as the most prosperous part of Lancashire to Ribble Valley - the only district to improve its position.
Lancashire as a whole has been categorised as a “mid-prosperity” region and the absolute prosperity scores across the county have also fallen in every district except Ribble Valley and Lancaster - indicating that the decline in other corners of the county has been in real terms as well as relative.
Eight of Lancashire’s 14 local authority areas appeared in the top half of the 2011 version of the league table of 379 councils, with three others missing out by only a handful of places.
However, ten years on and the slump in Lancashire’s prosperity has been so significant that just three parts of the county can claim a place in the upper half of the index - and none in the top 100.
Wokingham in Surrey has been deemed the most prosperous area of the UK, while Blackpool, which was the least prosperous location in Lancashire a decade ago, now bears that title for the whole of the country.
The index is intended to be used as a tool to support the government’s so-called “levelling up” agenda, but the report accompanying it warns that the process needs to be about “more than bridges and trains” - a reference to the perennial preoccupation with infrastructure as a method of boosting the prosperity of local areas.
To that end, the rankings were calculated on the basis of more than 250 individual indicators, split across 12 ‘pillars’ - of which infrastructure is just one. The others include living conditions, health, education, the natural environment and “social capital” - how cohesive a community is, based on the relationships between individuals and with institutions.
The authors of the report also claim that the current discussion about levelling up is too simplistic, with a skewed focus on making “crude distinctions” between north and south - and ignoring variations within regions as a result.
Daniel Herring, deputy head of the Centre for UK Prosperity at the Legatum Institute, told the Guardian that he hoped the index would help the different parts of Lancashire to identify the “binding constraint” on their prosperity - and so unlock a better future for them.
“We are really trying to understand what is actually holding back [some] areas and, in others, what’s pushing them forward.
“While even our index would point to some sort of North-South divide - [and] there are differences between towns and cities - we think the picture is more complex than that.
“When you start looking deeper down, you start seeing slightly different issues.
“We’re trying to bring together a broad range of people - local government, local entrepreneurs and civic society, but we also want to have a say in national policy and how that fits in.
“We’re trying to find a way of [ensuring everybody is] talking about the same things, rather than coming with a slightly different understanding of what’s going on [in an area].
"Everyone brings a different perspective on the problem and this index can help people see things and bring those perspectives together,” Mr. Herring said.
While the think tank report acknowledges that the UK is a generally prosperous country, it says that prosperity stalled in most regions in the latter half of the 2010s, with the North West being one of the worst affected areas.
In Lancashire, the index points to particular problems with the local economy - and employers struggling to attract the workforce they need. Nearly half of vacancies in the county are deemed ‘hard-to-fill’, while more than a third are due to skills shortages.
Less than two percent of businesses are seeking investment for new processes or expansion into overseas markets - the lowest rate in the country. The report suggests a need to focus on adult education, apprenticeships and training in entrepreneurship.
However, the county - and other non-metropolitan areas of the North West - are found to have some common strengths, including strong local government, low crime rates and favourable conditions for starting business, such as low property costs.
Chorley remains fourth in the ranking of non-metropolitan areas in the wider North West and its absolute prosperity score has fallen only fractionally.
The index found that living conditions, infrastructure and education had all improved over the last decade, but health, social capital and the local investment environment - measuring the availability of capital - had declined.
Chorley Council leader Alistair Bradley welcomed the district’s place near the top of the Lancashire prosperity league, but said that the fall relative to other parts of the country was a sign of “ a drain” of prosperity from the North to the South East over the last decade.
“It’s political to an extent - it might not be a deliberate policy, but it’s a symptom of government policies as a whole,” said Cllr Bradley, arguing that the decline was another reason for Lancashire to attempt to restart the currently stalled process towards devolution.
“Lancashire needs to get its act together to get the ability to demand devolved money and powers from the government - because without that, we won’t be able to reverse this trend of a deterioration in security and prosperity compared to the South East of the country.
“Locally, we need to be able to demonstrate that we are ready and able to take those powers on. We have shown we can work together over Covid - and so we need to be leading [the demand for devolution].
“We can’t sit here and wait, because in reality the government will never do it - fundamentally, the Treasury don’t like devolving things away from the centre.”
Mr. Herring accepts that it is unlikely that the UK will ever be ‘levelled up’ to some uniform standard - and so some areas will always be deemed more prosperous than others. However, he says hopes that the index will ensure that currently lower-ranked areas are not overwhelmed by the “scale of the challenge” facing them.
“The UK [is] are already starting from a high base - and the aim is to keep going and bring the areas that have been left behind further along. The index is a means to get there - we're not doing this so that one day Blackpool can be number one in the index, we’re doing this so the people of Blackpool can have better lives.”