I have used Columbia River Knife and Tool's (CRKT) Ritter RSK MK5. The knife was designed by Doug Ritter in collaboration with others. Doug is a survival equipment consultant here in the US.
Since the knife is mass produced, it is reasonably priced ($17.95 = £13.52?) and includes a tin. I purchased one to experiment with and like it. The blade is much smaller than an equivalent folder. Also, to use the knife, you "extend" the handle using the attached cordage and plastic "lock."
Here are the specs:
Blade: Length: 1.75"
Thickness: 0.12"
Steel: 3Cr13, 52-55 HRC
Knife: Overall length: 3.81"
Weight: 0.9 oz.
RSK Mk5 Sheath: (included with knife)
Material: Zytel
Length: 2.25"
Width: 1.47"
Weight: 0.3 oz.
The MK5 seems very robust. But I decided to carry a folder in my PSK. I wanted the longer blade length and decided I wouldn't use a knife that small for heavy tasks. I currently use a folder in my PSK. But I waiver between the more robust fixed blade and the longer blade of a folder.
Hope this helps!
- Woodsorrel