stupid tax question (UK)

xpost: the one time i had tax hassle (more than a decade ago, just after i graduated - part-time employer's fuck-up, it turned out, but deeply pissy for a skint 21-year-old) i went along to my local tax office in edinburgh and they rocked - astonishingly helpful about everything.

Q. My employee has lost (not received) the P45 can I issue a duplicate?
A. You must not issue a duplicate P45 under any circumstances.

Why the fuck not? I've either lost mine or they never sent me one or it got lost in the post and I'm stuck on some stupid tax code so I'm out £1000+.

Just spent ages on hold to HMRC only to fail the security questions because I got a digit wrong on my previous address postcode from 7 years ago and (this is the weird bit) because I don't know who I currently work for (I tried the parent company, the actual company and the intermediate parent company and they were all wrong - the parent company is what appears on my bank statement and was what I said first). No idea how I'm supposed to get this fixed.

you should probably write a letter to them if you can find an appropriate address. keep copies of everything, ask for a timely reply. i notice they've recently shut down the face to face access in our town, i'm assuming this is a national policy to avoid dealing with the results of whatever cuts in service they're undergoing. if you're not happy with your written response or you don't get one, your MP's surgery is probably your next move.

dunno what their online communications are like. alternatively just keep on holding on the phone system depending on yr patience.

I might be OK as my previous employers luckily don't know the rules and sent me a scan of my P45 anyway. Fingers crossed.

hullo UK ilx, i am currently invoicing for a small number of US dollars for a freelance writing job from the UK

i was told i need to fill in a W-9 but this cant be right as i am not a US citizen -- the likely equivalent for non-US citizens seems to be a W-8BEN

naturally the guidance for filling in this (quite short!) form is nightmarishly long and baffling -- does anyone (a) have practical experience of this process or (b) have an up-to-date link which will talk me through it sensibly

QUESTION IN THE MEANTIME: am i correct in believing that line 6 in the W-8BEN (which requests "foreign tax identifying number"), i just put my UK Tax reference number (as supplied by HMRC)?