For information only currently not available
Cam bolts fitted to the stock engine are actually incorrect for their application!! Especially the VVC engine due to the inherent imbalance the VVC  creating an eccentric cam path.
What does this mean ?? The additional loads and vibration can cause the bolts to relax a condition that is common with bolts used in this application. Use the incorrect bolt and this can occur with catastrophic damage to your engine. The majority of the early VVC engined cars had bolts that could relax and the original bolts were deemed unsuitable for the application. Indeed there was an early re-call /service document that addressed this issue..although many engines slipped through this net.
In simple terms, the bolts had a surface coating that wasn't suited for this application and after tightening to the 'correct' torque figure in fact they were under torqued due to the surface treatment and 'relaxed' and in some cases became loose with the cam gears moving and causing damage to valves and internal engine parts.
The bolts should never be re-used and you will not find any service or workshop manual stating this..why ?? I don't know but for the last 20 plus years, I have always used an upgraded bolt that due to the quality can be re-used.MG Rover did actually change the bolt to an uncoated bolt but never changed the part number and was not of the same quality as these bolts.
Some mechanics will re-use the old bolt without thinking of the consequences if it became loose and often smother it in a locking agent and I have seen the results of excess locking material between components causing the components to 'run out'.
I have read articles in MG publications showing old worn-out bolts being used and 'journalists' writing these articles getting it incorrect. These incorrect methods are then repeated by DIY enthusiasts and 'professionals' with the potential of major damage. 
Always remove old material from the cam using a cleaning M10 tap and use a degreasing agent to clean the internal threads and mating faces.
So this relatively innocuous component is IMO very important!!
Change yours at the earliest opportunity
NOTE the photo shows a locking agent in the kit. Unfortunately, we are not able to supply this due to the new postal rules.
Supplied as a kit of 2 bolts for Mpi engines £6.25 plus vat or 4 bolts for VVC engines. £12.50 plus vat
Note the new price of these have gone up dramatically since I last bought them!
I have adjusted the price accordingly and you have the option of 2 or 4 bolts.
Product update 11/2/23: Due to the high cost of these bolts I am looking at a redesign of the washer and bolt as a replacement unit.

Tech info
These self-locking hexagon flange bolts with ribbed flange are designated property class '100'. The flange bolts are case hardened in order to perform their self-locking function, and therefore cannot be classified as property class 10.9, although their tensile strength is at least 1040 MPa.
Special features of these self-locking flange bolts are:
•    The ribbed flange eliminates surface damage during assembly, prevents self-loosening and reduces relaxation. •    The flange enables built up forces under the bolt head to be spread over a larger area, consequently resulting in lower surface pressure. •    Large (oversized) or slotted holes can be covered by the flange. •    No other locking elements or washers are necessary.
The below table provides values for the advised assembly preload (FM in kN) and tightening torque (MA in Nm) for use with clamped materials as indicated 
M10 80-85 N/m  recommended 70N/M for this application.