You can get divorced for one reason only - the irretrievable breakdown of the marriage.
This can be established by:
Unreasonable behaviour; or
Adultery; or
Desertion; or
Separation
Many married couples do not have sex and are perfectly happy with their relationship.
If one person feels that not having sex is unreasonable, then that is grounds for divorce - provided it has caused a permanent breakdown in the marriage.
I seem to remember that 'refusal of sex from husband or wife' is listed under the terms for unreasonable behaviour.
In any case, as Ethel has said a divorce is granted under 'irretrievable breakdown'. If the marriage has broken down for whatever reason, it will be granted.
the marriage can only be voidable if it wasn't consumated, and only by the party who is being refused the sex; if he or she is happy without the marriage is still valid. I think the case here is withdrawal of sex, not refusal from the start, and the right grounds would be ireconcilable differences due to behaviour
1. Non-consummation is grounds for decree of nullity (not divorce) as marriage is voidable: section 12 of Matrimonial Causes Act 1973.
2. "withdrawal of sex" method not reliable contraception.