..In regards specifically to IELTS, from the table of approved providers you
will see that the lowest level of IELTS accepted by the UKBA as an
approved test is level 4. An applicant wishing to rely on an IELTS
qualification would therefore have to provide evidence that they have
obtained this qualification and have passed the speaking and listening
components at level 4.
For clarity, even though a person may be required to sit all four
components of an IELTS test, they would meet the English language
requirement by gaining a score of a minimum of level 4 in speaking and
listening only even if they failed the reading and writing components and
overall their final score was less than 4.
ie Reading – 1.5
Writing – 1.0
Speaking - 4.0
Listening – 4.0
Overall IELTS score – 2.5
The applicant is able to demonstrate they scored level 4 for speaking and
listening in an approved test by an approved provider therefore an
applicant could use such results to meet the English qualification for
partners...
Source:-https://www.whatdotheyknow.com/request/english_requirement_with_ielts_f