In a comment on Question 247321, Greenbriel suggested using a BIOS
password - which I have done.

He/she also uttered the dire warning 'Not to Forget It' ...

I haven't ... yet ... but, supposing I did ...

Is recovery hopeless?

(I have a vague recollection that there is a way ... but what is it?)

Hello, probonopublico:

  As you guess, yes, it's possible, there are several ways, but the
most common is to use a jumper in your motherboard, you will need to
check your motherboard documentation to know which jumper it is. You
simply need to change this jumper from one position to another and you
will get a blank BIOS, and of course, with no password at all.
  
  If you cannot find the jumper, the other method is to unplug the
system and to remove the internal battery, in a couple of hours
(depending on the system) the BIOS will be erased.
  
  If you don't want to erase the BIOS, which will also delete your
configuration (hd model, pci settings, etc), I suggest you to try
these backdoor passwords, but they may not work on your system:
  
At boot-up note the BIOS provider (Award, AMI, Phoenix, IBM, etc.) 
 
For Award BIOS’ try these backdoor passwords:

AWARD_SW
j262
HLT
SER
SKY_FOX
BIOSTAR
ALFAROME
Lkwpeter
j256
AWARD?SW
LKWPETER
syxz
ALLy
589589
589721
awkward
CONCAT
d8on
CONDO 
j64
szyx 
 
  
For AMI BIOS’ try these backdoor passwords:

AMI
BIOS
PASSWORD
HEWITT RAND
AMI?SW
AMI_SW
LKWPETER
A.M.I.
CONDO 
 
  
For PHOENIX BIOS’ try this backdoor password:

phoenix 

These solutions assume that you cannot boot onto your system, because
as you said, you want to prevent others from accessing your system,
not only to access the BIOS setup, in any case, if you can boot, you
can run some of those programs to crack your BIOS passwords:

Rempass
http://natan.zejn.si/rempass.html

BIOS password crackers
http://www.password-crackers.com/crack.html#AMI

You will find these links very useful:

BIOS PASSWORD AND LOCKED HARD DISK RECOVERY
http://www.pwcrack.com/bios.shtml

Get Past a Lost BIOS Password
http://www.avnonline.com/issues/200111/weeklytips/110101_tip4.shtml

And as a last suggestion, if you want to prevent others from accessing
your system, in my opinion, the best solution is to place your hard
drive on a removable system, so you can take your hard disk with you
when you leave the office, extreme, but effective, just a suggestion
;-)

I hope this information is useful to you, in any case, don't hesitate
to request for any clarification, we are here to help you!

Search Strategy

recovery lost bios password jumper
://www.google.com/search?hl=en&lr=&ie=UTF-8&oe=UTF-8&q=recovery+lost+bios+password+jumper

Regards.

What a brilliant answer!

And so quick, too.

Thank you very much or, as we say in the UK, muchas gracias.

(Sorry about the cedilla)