If I were to start a new company every year for 6 years
Company 1 LTD
..
..
..
Company 6 LTD

And then in year 6 HMRC starts up an IR35 investigation on company 6 LTD.
Are HMRC able to include Company 1-5 LTD in their investigation? or would they have to launch a separate investigation into each company? and thereby waste time/expense

Almost like creating an IR35 firebreak between the companies.
thoughts/comments?