it's complicated, but hopefully simple solution

History

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I joined a new start-up company in November 2017. There were no offices set up so we all remote worked, me at home. In February 2018 we were all told the money had run out, but investment was coming, so we kept working. Mid-March we were all put on notice of redundancy, which would be rescinded once (if) investment came through. By mid-April it was clear investment was not coming.
My last salary was paid in January, 2018.
I have not received my P45 as the company handling payroll have also not been paid so not working. I also believe they have not paid my PAYE, NI, or other benefits since January 2018 too.
I resigned mid-May and have now started a new role elsewhere.
I have consulted legal advice about this and am clear what I am doing / need to do.
We're talking a considerable amount (by my standards, anyway) of unpaid salary, not to mention impact it's had on family during +4 months without income.

Update

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However, the company are now asking for the laptop and printer back. Can I legitimately tell them I will enter into dialogue to return the equipment once they have entered dialogue to conclude the unpaid salary and benefits and have shown proof of their ability to do so?
Thanks in advance.