Passing parameters to SQL Queries loaded from a text file

I have a following issue when using SQL queries loaded from separately stored text files:

I have a following parameter in Power Query: TestParameter with a value of 5000003

When I use the parameter in the following query it works fine and fetches me the expected rows from the database table:

= Sql.Database("server", "database", [Query="SELECT * FROM VBPA WHERE [Osobní číslo] = '" & TestParameter & "'"])

However, when I put the SQL query SELECT * FROM VBPA WHERE [Osobní číslo] = '" & TestParameter & "' into a separate .txt file, load it as a text parameter SQL_test and write the query as follows, it fetches an empty table:

= Sql.Database("server", "database", [Query=SQL_test])

If I try to put the TestParameter value 5000003 directly into the SQL_test text parameter as follows, it works fine and the query = Sql.Database("server", "database", [Query=SQL_test]) fetches the relevant rows from the database table:

SELECT * FROM VBPA WHERE [Osobní číslo] = '5000003'

The problem therefore seems to be with the parameter TestParameter inside the SQL_test parameter, as PowerQuery seems to be unable to evaluate it as a parameter.

Any ideas how to make this work and is it even possible?