You may have noticed that there's a bit of a bug going round at present - leaving aside the fact that it has exposed how fragile our society seems to be, media hysteria and general paranoia mean that despite being classed as an 'essential service', the mail service has been hit pretty hard.
TL;DR - mail services are pretty much fucked at present; expect delays - for international orders, particularly to the US, expect some major delays. Based on my experiences, mail to the EU is still moving pretty well (even to Italy ...)
Although Royal Mail have been reluctant to admit it, there is currently a backlog of over 2 million parcels (some estimate as many as 10 million) at various processing hubs round the country - given reduced staffing levels and physical distancing requirements, this stuff is going to take a while to clear. That being said, I've had relatively few issues with Royal Mail Signed For deliveries thus far.
However although my local processing centre seems to be clearing things in a timely manner, the same cannot be said for sorting offices elsewhere - if your local sorting office has a particularly bad backlog then expect delays; the 1-2 working days delivery time for First Class Signed For is a guideline only; if you want a guaranteed service then you'll need to stump up for Special Delivery.
International mail is a different matter entirely - unless you're a courier who happens to have its own air fleet (eg. UPS, FedEx, DHL) then mail generally travels in the hold on commercial flights and, guess what, the number of commercial flights has been severely reduced - true, there are the occasional cargo-only flights, but these appear to be the exception rather than the rule at present.
Mail to and from the US seems to be particularly affected at present - as I write this, I've been waiting nearly 6 weeks for a consignment of boards and panels (several hundred quid's worth, yet) to arrive from the US. I'm not holding my breath and I fully expect that I'll need to chase USPS for compensation. Won't that be fun? Things are bad enough, with regards to the availability of flights (or lack thereof) that USPS are now sending European mail by sea (doesn't appear to affect the UK ... yet) and there appears to be a backlog of US-bound mail at the UK distribution hub at Heathrow (don't ask how I found out about this ...)
Now, here's the thing ...
I send all of my orders using a tracked service.
All of them.
Even if you're only ordering a single PCB, it'll go tracked and you'll be sent a tracking number via email once your order has been fulfilled. Keep this number handy, 'cos you may need it.
Another very important point to consider:
ONCE I HAVE POSTED YOUR PACKAGE, I HAVE ABSOLUTELY NO CONTROL OVER WHAT HAPPENS TO IT WHILST THE MAIL CARRIER HAS IT.
Seriously, once your stuff has been accepted by Royal Mail it is out of my hands in both the figurative and literal sense. That's where your tracking number comes in handy.
You can track your package via the Royal Mail's track and trace website - just enter your tracking number and the job's a good'un. For UK orders, your package will be tracked from acceptance at my local PO to delivery, bearing in mind that there are certain protocols in effect because of the aforementioned malady.
For international orders, Royal Mail track and trace will only work until your package has left the UK. After this point, once your package has been accepted by your national carrier you'll be able to track it via their website using the same tracking number. If the RM site states that your order has left the UK but it isn't recognised by your national carrier, then it is either in transit or languishing in customs, in which case see the above point regarding me having no control over stuff once it has been posted.
One final point - Royal Mail do not consider a package to be 'lost' until a certain time after it was supposed to be delivered. For domestic mail this is 18 working days (just over 3 weeks), or 25 working days (nearly 5 weeks) for international mail.
Until the appropriate time has elapsed, I will not be able to pursue compensation from Royal Mail. If you wish to make your own enquiries and/or claim with your national carrier then feel free to do so - in such cases I'm more than willing to send you a copy of your proof of postage via email.
UPDATED TO ADD: although Royal Mail have stated that they will be suspending Saturday deliveries from May 2nd, this doesn't appear to affect tracked items.