Where a property is owned jointly by a married couple, the rent is split on a 50:50 basis by default unless it is actually owned in proportions other than 50:50 and HMRC are advised by the couple through the completion and submission of a form 17
Where a property is owned by more than individual and they are not married, the rental income can be split as the owners wish regardless of the proportions in which it is owned which is what you did with your son.
From the point in time that your son became the sole owner, he should have been disclosing the rental income in his own tax returns even if he mandates it to you.
When you signed over your 50% share to your son, that was a disposal for Capital Gains Tax purposes at the open market value of that share so each of you and your wife will almost certainly have a capital gain to disclose given that you bought the property in 2002. The first £11,000 of gains an individual made in 2014/15 was exempt from CGT. The equivalent figure was £10,900 for 2013/14.
The gift of the 50% share to your son is also a potentially exempt transfer for Inheritance Tax purposes which will fall out of your own and your wife's estates so long as you each live for at least seven years after making it. After three years, the potential IHT charge tapers away as you can see here
. The nil-rate IHT band is also first used against gifts made in the seven years before death.
I hope this clarifies your position but let me know if you have any further questions.