Highly Important from England.
ARRIVAL OF THE STEAMER "EUROPA."
Great Excitement over the Mason and Slidell Affair.
A Queen's Messenger Sent with Dispatches to Lord Lyons to Demand the Restoration of the Persons of the Southern Envoys Views of the British Press

HALIFAX, Dec. 15.-The Europa arrived here to-day from Liverpool, on the 30th ult., and Queenstown on the 2d inst., where she was detained until Monday, by order of the British government. She has the Queen's messenger on board, with dispatches for Lord Lyons.

LONDON, Dec. 1.-The Observer states that the government will demand from President Lincoln and his Cabinet the restoration of the persons of the Southern envoys to the British government.
       Yesterday afternoon after five o'clock her Majesty held a Privy Council at Windsor Castle. Three of her Majesty's ministers, including the First Lord of Admiralty and Secretary of State for War, traveled from London to Windsor by special train to be present. Previous to leaving town, the three ministers bad attended a Cabinet council at Lord Palmerston's official residence.
       The Observer says a special messenger of foreign affairs has been ordered to carry our demands to Lord Lyons, and will proceed by packet from Queenstown to-day. The public will be satisfied to know that these demands are for an apology, and to insist on a restitution to the protection of the British flag of those who were violently and illegally torn from that sacred asylum.
       The Observer adds: "There is no reason why they should not be restored to the quarter-deck of a British Admiral at New York, or Washington itself, in the face of ten or twelve men of war, whose presence in the Potomac would render the blustering Cabinet at Washington as helpless as the Trent was before the guns and cutlasses of the San Jacinto. It is no fault of ours if it should come even to this."
       Arrangements for increasing the force in Canada are not yet complete, but in a very few hours everything will be settled. In the meantime a large ship, the Melbourne, has been taken up and is now being loaded with Armstrong guns, some 80,000 Enfield rifles, ammunition and other stores at Woolwich. It is not impossible that this vessel will be escorted by one or two ships of war. The rifles are intended for the Canadian military, and strong reinforcements of field artillery will be dispatched forthwith.
       The London Times' City article of the 30th says: "The position of the Federal States of America is almost identical in every commercial point of view with that which was occupied towards us by Russia before the Crimean War. Russia had a hostile tariff while we looked to her for a large portion of our general supply of breadstuffs, but there is this peculiarity in our present case, that the commencement would be by breaking up the blockade of the Southern ports, at once set free our industry from the anxiety of a cotton famine, and send prosperity to Lancashire through the winter. At the same time we shall open our trade to eight million in the Confederate States who desire nothing better than to be our customers.
       "At a privy council on Saturday an order was issued prohibiting the export from the United Kingdom, or the carrying coastwise, of gunpowder, saltpetre, nitrate of soda and brimstone."
       The Times has no hope that the Federal government will comply with the demands of England. . . .
       It was regarded when the Europa left that there was a hopeful look, and consols and cotton (stocks) bad slightly improved but, after digesting the tone of the American press, a reaction set in, and fears were entertained that the Washington government would justify the act.
       The English journals were very bitter and hostile, continuing to treat the affair as an intolerable insult. . . .