What is it with this company?
I sent a letter 1st class signed for last Saturday and, if their site is to be believed, it's still at the    post office where I posted it as there are no updates other than 'We've got it'

I often see a notification along the lines of the tracking isn't updated again until they attempt delivery.

I've seen the cop out "won't be updated until they've attempted delivery"
They've had 4 working days to deliver a 1st class signed for letter.
And they've just put the cost up - again.

If you send it 'signed for', that's what you get. If you're lucky, they'll record the signature, and you can see that.
I've sent stuff that way to eg. DVLA, and I've had the response through the post while the outbound one is still showing as awaiting delivery.
You need to send it by a trackable service like Special Delivery if you want to follow its journey.

I respond as a person who spent 18 years within a Royal Mail main sorting office(before privatisation).

Before privatisation it was a public service. There was a pride in ensuring as far as was possible 1c mail reached it's destination the next day.
I read recently that postal tariffs have doubled since privatisation, and yet the Q of S has plummeted.

In the face of increasing competition from couriers, incredibly they have decided to refuse certain items within the postal system. Items they have been happy to accept in the past!

Sadly the business has pretty much gone to the dogs.

It saddens me, as I was proud to work for them, serving the general public.

I've had this problem too - it seems if you want to follow the progress these days, it needs to be tracked and signed for... 

I'm a little old-fashioned. I don't follow up this track business. If I order something by mail, I sit back and forget about it, get on with other stuff like cleaning the toilet and so on,  then I get a pleasant surprise when it arrives.