The Cycle to Work scheme is not free! Basically, your employer pays up to £1000 for the bike and accessories. The cost is deducted from your wages over a period (based on your gross wage before tax and NI are paid, so you pay tax and NI on the lower wage which saves you money). The employer owns the bike. After the period is over, you can continue to use the bike or you can buy it based on a percentage of what the bike is worth now. I think some employers give the bikes to their employees.
The employer has to be a member of the scheme.
Also theoretically the employee is responsible for insuring his/her bike so you may still have to pay if your bike is stolen. So it is worth checking if you have contents insurance whether the costs of a bike are covered. They usually are, but it may only cover a proportion or a reduced amount of the cost.
British Cycling Membership covers liability cover and will give you a 10% discount at Halfords which other suppliers may match. It also gives you reduced price full bike insurance BS membership is from £23 per year.