Where sharia law is the law of the land that system obviously is relevant. Where sharia law is not in precise agreement with the law in the country concerned then sharia law is irrelevant and legally unenforceable. Those who want to observe sharia law to appease their conscience are indulging in a hobby/belief which should never be opposed unless either that involves adversely affecting someone in contradiction to their rights under the indiginous law and regulations, or else if the individual in question is in some way thereby engaged in something that is against the laws and regulations in that country - for example slaughtering a sheep in the UK by slashing its throat and letting the blood into the neighbourhood gutter. If someone wants to observe a practice, sharia law or anything else, that is of no consequence to others and is entirely legal, then that should be fine. Anyone who wants to feel bound by a sharia marriage vow will obviously only obtain spitritual release through the same process - but once a legal civil divorce is obtained then no rightful law in the UK binds that person to their former spouse, it is only in the mind that this person remains bound until the entity they recognise has released them. Legally it matters not a jot which higher authoirity they choose to imagine (hloy man, god, fairy or whatever) - they are no longer married anywhere except in their heads.