I know VEng is an up and coming option within the RLC, although as to the qulaifying critiera I cannot help. I believe that Ammunition Techncians are one of the groups aimed at - perhaps have a stab in the RLC Forum.
Having spoken to a few guys about this I am not entirely convinced that it will be well received, the way I understand it (and I could be completely off track here), is that a soldier will carry on as per the last 22 years of his career for an extra 3, 5 or 7 years. The reason I don't believe it will be that well received is, as I understand it, a soldier will effectively be doing the same job he has always done for Â£x less, as he will be at the immediate pension point at the commencement of his VENG and would be entitled to Â£x per month irrespective of whether he stayed in the army or not.
Like I say, you may want to ask in the RLC forum for a more comprehensive and authoratative answer.