The envelope process removes the possibility of somebody knowing the details of a tender and communicating this information to a rival bidder. For larger contracts, you should follow this procedure. The potential drawback with this process for parish councils is that a lack of clarity in the specification of the contract may result in bids that are not truly comparable. I saw a situation recently where a small landscaping project included the supply and installation of a row of wooden posts to keep vehicles off an open space. The size of the posts was specified, but no further detail was provided. The tenders received included everything from sawn softwood posts at about £10 each to proper hardwood roadside bollards with reflectors at about £50 each, so the cheapest quote was for a less desirable job, but still within specification. Using a consultant to specify the project avoids all potential confusion, but comes at a cost.