Create 2 shipping zones.
One is UK only, the other is Rest of the World.
Using the Flat Rate module, apply the shipping to your UK zone only.
And to make it real easy, run this through your admin>tools>install sql patches but BACKUP first.
//to create a Rest of the World Zone
INSERT INTO `geo_zones` (`geo_zone_id`, `geo_zone_name`, `geo_zone_description`, `last_modified`, `date_added`) VALUES (20, 'RoW', 'All Countries Except the UK', NULL, '2006-07-03 12:32:13');
INSERT INTO `zones_to_geo_zones` (`zone_country_id`, `zone_id`, `geo_zone_id`) VALUES (1, 0, 20),
(2, 0, 20),
(3, 0, 20),
(4, 0, 20),
(5, 0, 20),
(6, 0, 20),
(7, 0, 20),
(8, 0, 20),
(9, 0, 20),
(10, 0, 20),
(11, 0, 20),
(12, 0, 20),
(13, 0, 20),
(14, 0, 20),
(15, 0, 20),
(16, 0, 20),
(17, 0, 20),
(18, 0, 20),
(19, 0, 20),
(20, 0, 20),
(21, 0, 20),
(22, 0, 20),
(23, 0, 20),
(24, 0, 20),
(25, 0, 20),
(26, 0, 20),
(27, 0, 20),
(28, 0, 20),
(29, 0, 20),
(30, 0, 20),
(31, 0, 20),
(32, 0, 20),
(33, 0, 20),
(34, 0, 20),
(35, 0, 20),
(36, 0, 20),
(37, 0, 20),
(38, 0, 20),
(39, 0, 20),
(40, 0, 20),
(41, 0, 20),
(42, 0, 20),
(43, 0, 20),
(44, 0, 20),
(45, 0, 20),
(46, 0, 20),
(47, 0, 20),
(48, 0, 20),
(49, 0, 20),
(50, 0, 20),
(51, 0, 20),
(52, 0, 20),
(53, 0, 20),
(54, 0, 20),
(55, 0, 20),
(56, 0, 20),
(57, 0, 20),
(58, 0, 20),
(59, 0, 20),
(60, 0, 20),
(61, 0, 20),
(62, 0, 20),
(63, 0, 20),
(64, 0, 20),
(65, 0, 20),
(66, 0, 20),
(67, 0, 20),
(68, 0, 20),
(69, 0, 20),
(70, 0, 20),
(71, 0, 20),
(72, 0, 20),
(73, 0, 20),
(74, 0, 20),
(75, 0, 20),
(76, 0, 20),
(77, 0, 20),
(78, 0, 20),
(79, 0, 20),
(80, 0, 20),
(81, 0, 20),
(82, 0, 20),
(83, 0, 20),
(84, 0, 20),
(85, 0, 20),
(86, 0, 20),
(87, 0, 20),
(88, 0, 20),
(89, 0, 20),
(90, 0, 20),
(91, 0, 20),
(92, 0, 20),
(93, 0, 20),
(94, 0, 20),
(95, 0, 20),
(96, 0, 20),
(97, 0, 20),
(98, 0, 20),
(99, 0, 20),
(100, 0, 20),
(101, 0, 20),
(102, 0, 20),
(103, 0, 20),
(104, 0, 20),
(105, 0, 20),
(106, 0, 20),
(107, 0, 20),
(108, 0, 20),
(109, 0, 20),
(110, 0, 20),
(111, 0, 20),
(112, 0, 20),
(113, 0, 20),
(114, 0, 20),
(115, 0, 20),
(116, 0, 20),
(117, 0, 20),
(118, 0, 20),
(119, 0, 20),
(120, 0, 20),
(121, 0, 20),
(122, 0, 20),
(123, 0, 20),
(124, 0, 20),
(125, 0, 20),
(126, 0, 20),
(127, 0, 20),
(128, 0, 20),
(129, 0, 20),
(130, 0, 20),
(131, 0, 20),
(132, 0, 20),
(133, 0, 20),
(134, 0, 20),
(135, 0, 20),
(136, 0, 20),
(137, 0, 20),
(138, 0, 20),
(139, 0, 20),
(140, 0, 20),
(141, 0, 20),
(142, 0, 20),
(143, 0, 20),
(144, 0, 20),
(145, 0, 20),
(146, 0, 20),
(147, 0, 20),
(148, 0, 20),
(149, 0, 20),
(150, 0, 20),
(151, 0, 20),
(152, 0, 20),
(153, 0, 20),
(154, 0, 20),
(155, 0, 20),
(156, 0, 20),
(157, 0, 20),
(158, 0, 20),
(159, 0, 20),
(160, 0, 20),
(161, 0, 20),
(162, 0, 20),
(163, 0, 20),
(164, 0, 20),
(165, 0, 20),
(166, 0, 20),
(167, 0, 20),
(168, 0, 20),
(169, 0, 20),
(170, 0, 20),
(171, 0, 20),
(172, 0, 20),
(173, 0, 20),
(174, 0, 20),
(175, 0, 20),
(176, 0, 20),
(177, 0, 20),
(178, 0, 20),
(179, 0, 20),
(180, 0, 20),
(181, 0, 20),
(182, 0, 20),
(183, 0, 20),
(184, 0, 20),
(185, 0, 20),
(186, 0, 20),
(187, 0, 20),
(188, 0, 20),
(189, 0, 20),
(190, 0, 20),
(191, 0, 20),
(192, 0, 20),
(193, 0, 20),
(194, 0, 20),
(195, 0, 20),
(196, 0, 20),
(197, 0, 20),
(198, 0, 20),
(199, 0, 20),
(200, 0, 20),
(201, 0, 20),
(202, 0, 20),
(203, 0, 20),
(204, 0, 20),
(205, 0, 20),
(206, 0, 20),
(207, 0, 20),
(208, 0, 20),
(209, 0, 20),
(210, 0, 20),
(211, 0, 20),
(212, 0, 20),
(213, 0, 20),
(214, 0, 20),
(215, 0, 20),
(216, 0, 20),
(217, 0, 20),
(218, 0, 20),
(219, 0, 20),
(220, 0, 20),
(221, 0, 20),
(223, 0, 20),
(224, 0, 20),
(225, 0, 20),
(226, 0, 20),
(227, 0, 20),
(228, 0, 20),
(229, 0, 20),
(230, 0, 20),
(231, 0, 20),
(232, 0, 20),
(233, 0, 20),
(234, 0, 20),
(235, 0, 20),
(236, 0, 20),
(237, 0, 20),
(238, 0, 20),
(239, 0, 20),
(240, 0, 20);
This was a simple change to the US v RoW snippet that Linda posted elsewhere to make this UK friendly