A couple of days ago I spent ages researching the term and I have used it in my translation. I just hope it's right ;-)

Special requirements for in-house providers - Annex 2
Contracts awarded to in-house providers by the County Council
(1) It is the Council’s policy to invite in-house providers to tender for works, supplies or services, where appropriate.
(2) A formal letter of acceptance shall be sent to the in-house provider by the Council in accordance with section 23 of the code. At no time shall a contract executed as a deed (under seal) be arranged. No contract can exist between the Council and the in-house provider, but all work shall be carried out on the understanding that the in-house provider will comply with the requirements of the conditions of the contract and the specification under which the work was tendered.

https://shareweb.kent.gov.uk/Documents/business/business-con...

The Government will, as I said in my statement, continue for the time being to fund wages, salaries and payments to contractors and suppliers where that is necessary for the provision of key public services. That is to give the official receiver the time to arrange, in an orderly fashion, the transfer of service provision, either to a new contractor or to an in-house provider within Government.

https://www.theyworkforyou.com/debates/?id=2018-01-15b.623.4

The in-house providing exception is based on two requirements: the public authority must (1) exercise control over the in-house provider which is similar to that which it exercises over its own departments and, at the same time (2) the in house provider must carry out the essential part of its activities with the controlling public authority or authorities. These requirements have been the subject of a broad analysis in a number of papers published in the Public Procurement Law Review by Kurt Weltzien in 2005, by Fotini Avarkioti in 2007 and by Toni Kaarresalo in 2008.

https://www.robertocavalloperin.it/wp-content/uploads/39-Con...

The marketing tools and applications have been developed with the objective of endorsing and modernizing Isdefe's Coporate Image, enhance its positioning and perception as in-house technical services provider of the Spanish General Administration, as well as supporting the commercial functions, focusing its actions to boost business oportunities in new or existant markets to guarantee the company' s sustainability.

https://www.isdefe.es/node/228?language=es

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Note added at 7 hrs (2019-09-23 00:18:22 GMT)
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Could anyone help me with the expression "medio propio y servicio técnico"?
It relates to an institution which claims to be independent from the State and often describes itself as "La condición de medio propio y servicio técnico de la Administración General del Estado"

or as I gather, something similar to "the status of being self-sufficient but receiving technical service from the Central Government"

Can anyone provide an opinion or a confirmation?

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Es un término relacionado con las administraciones públicas, cháchara técnica pública para que nos entendamos y es la versión española del concepto anglosajón "in house providing"; capacidad auto organizativa, suministro interno.
Resumiendo "medios propios y servicio técnico" = recursos auto gestionados.

https://forum.wordreference.com/threads/medio-propio.2809601...



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Note added at 6 days (2019-09-29 14:14:50 GMT) Post-grading
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Thanks for the points! Although Guillermo's solution is right, it would have been too long to use in my translation, where 'medio propio y servicio técnico' was mentioned at least half a dozen times!