It has long being our view that if a person dies abroad it makes economic sense to have him, or her, cremated in the country of death and the ashes brought back to this country. (Note that some travel insurances offer to fly the body back or a contribution towards the cremations costs abroad in lieu. If you have to pay to bring the body back the charge is frightening - basically airlines dislike carrying bodies.) To date nobody has had any problems with doing this.
Disposing of ashes in this country is remarkably simple and there are few restrictions. Obviously if on privately owned land the owner’s permission needs to be sought and the three favourite classes of such land are football pitches, golf courses and horse racing courses. Policies vary and some clubs, such as Manchester City, have their own garden of remembrance. Bear in mind, if scattering on a golf course, that if you wish to revisit the site unless you are a member in your own right you may not be able to do so. Common land, also, may not always be used as the rights are normally restricted.
Despite what you may have seen on Only Fools and Horses there are no restrictions on scattering ashes into rivers provided that no plastic is disposed of as this does not degrade. The Environment Agency has a handy leaflet on the matter and other items such as home burials.
A word of warning on cremated remains. They are not bone meal and have far too high a level of phosphates to promote growth. Placing them in the earth and planting a rose will not work - it will merely kill the rose. A number of ornamental gardens, even public ones, have started to ban the scattering of ashes and popular mountain top sites are causing additional problems for the National Parks as it is affecting the local flora - and at some sites the plants are unique.
It is when you wish to scatter the ashes abroad that problems can occur as, unlike Britain, there are numerous regulations and some, such as the Philippines, insist that the ashes be treated in the same manner as a dead body. The best advice is to contact the embassy/embassies before you do any planning. You will almost certainly require various certificates in English and notarized translations, frequently charged at so much per word. If you are considering a ‘world tour’ disposing of a portion of ashes here and there the cost of documentation alone could be daunting, let alone different regulations in each country.
A useful site, that explores the above matters and others more fully and which has a direct link to the Environment Agency’s leaflet, is www.scattering-ashes.co.uk