Image copyright Creative Commons Image caption Interserve holds the contract for cleaning Network Rail stations

Interserve, one of the UK's largest providers of public services, is urging shareholders to back a rescue deal or the firm could face administration.

Last month it reached a deal with creditors to prevent its collapse.

But if shareholders reject its debt-for-equity-swap plan in a vote this Friday, Interserve's lenders could apply for a pre-pack administration.

This would mean the firm avoiding a Carillion-style collapse, but would wipe out existing shareholders.

A pre-pack administration enables a company to sell itself, or its assets, before it appoints administrators - who then take over the running of the business to protect creditors.

In a pre-pack, the lenders take 100% of the business.

Watered-down holdings

Interserve's rescue plan involves cutting its debts from more than £600m to £275m by issuing new shares. These will then be swapped with creditors for debt.

However, if shareholders do vote to approve the rescue deal, which would hand 95% of the firm to lenders, it would leave them with with heavily watered-down shareholdings.

Interserve's largest shareholder, Coltrane Asset Management, is critical of the deal and is threatening to block it unless there is a better deal for shareholders.

Interserve sells services, including probation, cleaning and healthcare, and is involved in construction projects.

Share plunge

Under the rescue deal, Interserve will also keep its most profitable division, its RMD Kwikform construction business, loading £350m of debt onto its balance sheet.

The firm had considered spinning the unit off to its lenders to raise money.

Analysis: BBC Business editor Simon Jack

If the company collapses on Friday - this is what will happen.

Accountants EY will be appointed administrators, they will then sell the company for a nominal amount to the current lenders (a mixture of banks and bond holders) who will own 100% of the new company.

The banks would look to sell off different parts of Interserve's business in due course.

The board does not expect any interruption to the company's underlying contracts or any immediate job losses.

Read more from Simon here.

This is the second rescue deal for Interserve, with the company refinancing its debt in March last year.

Its troubles have been blamed on cancellations and delays in its construction contracts as well as struggling waste-to-energy projects in Derby and Glasgow.

The firm's shares have plunged over the past year, currently trading at 14.6p each. Just over a year ago, the shares were worth 100p each.

Following Carillion's collapse, the government launched a pilot of "living wills" for contractors, so that critical services can be taken over in the event of a crisis. Interserve is one of five suppliers taking part.

What does Interserve do?

From its origins in dredging and construction, the company has diversified into wide range of services, such as healthcare and catering, for clients in government and industry.

At King George Hospital in east London, for instance, Interserve has a £35m contract for cleaning, security, meals, waste management and maintenance.

Its infrastructure projects include improving the M5 Junction 6 near Worcester, refurbishing the Rotherham Interchange bus station in Yorkshire, and upgrading sewers and water pipes for Northumbrian Water.

Interserve is also the largest provider of probation services in England and Wales, supervising about 40,000 "medium-low risk offenders" for the Ministry of Justice.