I'd tend to use the terms instruct and advise to mean essentially the same thing. If I buy some flatpack furniture it will contain instructions as to how to put it together. If I choose to ignore those instructions I can do so. They are only advisory.
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There's a letter in todays Guardian which very clearly indicates that in all this business with the court decision the government hasn't got a clue. Read the two bits in bold. Straight out of Yes, Prime Minister. But I'd challenge Sir Humphrey to reconcile those two sentences...:

• Neither your news reports nor letters from readers have made mention of perhaps the most relevant text on the referendum. This is a clear statement by government on parliament's role, found in the "Government response to the report on Referendums in the United Kingdom", comprising a report by the House of Lords select committee on the constitution (HL Paper 99), published on 30 September 2010, replying to the committee report issued on 7 April that year.

In a letter to the committee, Mark Harper MP wrote: "I welcome the report … and, given the profile and importance of the subject, the government has considered its response carefully in light of the recent introduction of the parliamentary voting system and constituencies bill."

In its substantive response to recommendations the government asserted: "Under the UK's constitutional arrangements parliament must be responsible for deciding whether or not to take action in response to a referendum result."

Yet Downing Street's response to the high court judgment was to say: "The government is disappointed by the court's judgment. The country voted to leave the European Union in a referendum approved by act of parliament. And the government is determined to respect the result of the referendum. We will appeal this judgment."
Dr David Lowry
Stoneleigh, Surrey