* COVID-19, energy crisis, rates failed to spark default wave

* Firms revamping business models, under pressure to consolidate

* Low share prices make M&A unattractive for fund sellers

* M&A revival hopes pinned on recent ION's Prelios deal

MILAN, March 20 (Reuters) - Europe's debt collectors have gone from feast to famine amid a collapse in the number of bank loans turning sour.

Companies that recover unpaid bank debts, and which thrived in the aftermath of the euro zone sovereign debt crisis, are rethinking their business models and examining tie-ups with rivals after COVID-19, an energy crisis and two-decade-high interest rates failed to unleash a new wave of loan defaults.

Banks in Europe's south have largely completed the clean-ups that once fed the bad loan bonanza and pulled in overseas investment firms such as Apollo, Cerberus, PIMCO, Elliott and Lone Star, while government support measures have helped keep companies and households on their feet.

Non-performing loans (NPLs) have held at 1.8% of total bank loans in Europe for six straight quarters, official data show.

In Italy, the continent's biggest market for bad debts, sales last year totalled 31 billion euros ($34 billion), a third of the 2018 peak. Back then, virtually all disposals came from banks, while more than half of the total in 2023 were re-sales.

Shares in some of the continent's main players including Sweden's Intrum - Europe's biggest debt collector - and Italian leader doValue hit record lows this month as investors weigh whether efforts to restructure their business can work. Both companies declined to comment.

"Several players are undergoing a metamorphosis," said Francesco Cataldo, a director at consultancy PwC Strategy& in Milan.

Keeping loan managers in activity is important because they can provide a new lease of life to assets - sometimes businesses or properties - that are tied up in insolvency or restructuring procedures, helping economic growth.

HIGHER DEBT COSTS, LOWER BAD LOAN FLOWS

Many collectors have not only stopped buying new impaired loans now that debt costs make that economically unviable, but are also shedding assets bought in the past.

Intrum, whose shares are down 78% this year, in January sold a nominal 33 billion euro loan portfolio to Cerberus, retaining management of the loans and using the cash to cut its recently downgraded debt. It is working with advisers to improve its debt position.

Similarly, Italy's Mediobanca in October quit the NPL investment business and sold its arm that held a nominal 6.5 billion euros in bad loans.

Intrum's 'capital light' model was embraced last week by Italian state-owned bad loan manager AMCO when it presented a new three-year strategy, saying it would reduce loans under management and cut its financial debt to zero.

"Banks have minimal impaired loan levels and high capital buffers," AMCO said, pointing to structurally lower new bad loan flows and mounting competition in the sector, where firms must comply with new European Union regulation by mid-2024.

Banks' healthy loan books also threaten collectors that never invested directly in NPLs, relying instead on contracts with lenders outsourcing debt recovery. As they gradually expire, those multi-year contracts may not be renewed.

Italy's doValue, which is backed by Japan's SoftBank Group and has a key UniCredit contract ending in 2025, is expected to outline alternative revenue sources when it presents a new strategy on Thursday.

Its shares have lost 47% this year after it reported a 2023 loss on an impairment it booked on its operations in Spain, where it lost a major contract in 2022.

M&A REVIVAL

In a crowded market, mergers offer an obvious way for debt collectors to reduce competition and increase scale.

But investment bankers say the poor performance of listed bad loan specialists renders valuations unattractive for sellers.

Multiple deals have been explored but failed to go through in recent years, with varied business models making it hard to set price tags that would spur big investment funds to sell the debt servicers they bought in the boom times, the bankers said.

Hopes of an M&A revival are now pinned on fintech group ION's 1.3 billion euro acquisition of Italian loan manager Prelios from U.S. hedge fund Davidson Kempner.

Valued at around nine times its core profit, Prelios could set a benchmark for future deals, two industry sources said.

ION gained government clearance this month to buy Prelios and now needs central bank approval. It is then expected to merge Prelios with Cerved, another NPL business it bought in 2021.

Italian authorities fret over the troubles of a sector that is key for the billions of euros of loans offloaded by banks, people familiar with their thinking said.

"Though new NPL inflows are low, we shouldn't forget that in Italy alone some 250 billion euros in problem debts are still largely out there. Behind those loans there are businesses and families whose debt issues remain unsolved," Cataldo said.

($1 = 0.9144 euros)

(Reporting by Valentina Za; Editing by Tommy Reggiori Wilkes and Mark Potter)