The value of a BSc (Hons.) is above that of a HND and normal BSc but lower than a PHD. The final grade is awarded in the following range: 

The final grade is calculated from the mean average total of grades. Each module usually consists of two assignments and an exam, of which, 18 modules are taken over a three year period. If a module is failed it can be re-taken but the maximum grade attainable is 40%. 

The BSc (Hons.) in Computing concentrates equal weight on programing and design as well as  research and reports / essay writing. Most assignments required all these at the same time so it's hard work! Unlike the HND assignments don't usually come with a marking scheme so arguing marks with a lecturer is harder. 70% marks seem to be awarded if you carry out 100% of the work correctly. Any extra above this seem to come from extras provided above and beyond what was asked for. I've managed a 90% and two 85% in assignments but most are around the 70% mark. You really need to make your work stand out from the crowd! The exams are tough though and usually bring the average module grade down.

The HND didn't prepare for the level of detail needed on report / essay work, so the first few modules are in the 2ii range. Luckily, two of these can be replaced by HND exemptions but unfortunately having done a HND, module choice is severely limited and you end up taking hard / boring / unpopular ones.  
Allowing for exemptions, this calculates to an average of 70.2% which is just about a 1st.