Adds further details, background from paragraph 2

March 4 (Reuters) - Banco Santander SAN.MC is owed between 200 million pounds ($267 million) and 300 million pounds by a company tied to Market Financial Solutions, a UK mortgage lender that collapsed last week, Bloomberg News reported on Wednesday, citing a person familiar with the matter.

The Spanish lender's exposure is secured against a portfolio of mortgages, the report added.

Banco Santander declined to comment.

The figure compares to the 495 million pounds owed to Barclays BARC.L, 200 million pounds to Elliott Management and 400 million pounds owed to Apollo Global Management 's APO.N Atlas SP Partners unit.

Banks and private credit funds are scrambling to assess their exposure to MFS after the little-known lender was placed into administration amid allegations of financial irregularities and mismanagement.

London-based MFS specialised in complex property-backed loans. It had applied for administration, a form of UK insolvency protection, after it ran into difficulties.

($1 = 0.7481 pounds)

(Reporting by Fabiola Arámburo in Mexico City; Editing by Sahal Muhammed)

((Fabiola.Solano@thomsonreuters.com))