A Hertfordshire-based maker of a live tracking device for pets has smashed an equity crowdfunding target, with tennis star Andy Murray revealed as one of the investors.

The business behind Dog Tracker Nano has returned to Seedrs for the second time to raise a minimum investment of £70,000 in return for a 5 per cent equity stake.

It has already exceeded 115 per cent of the target, raising more than £81,000 from 110 investors.

Dog Tracker Nano is described as a small, lightweight and waterproof dog tracking system used to monitor activity and fitness.

The product was officially launched in October 2015 following an overfunded round on Seedrs, and went on to sell more than 500 pre-orders in ten weeks. The business now has sales - or commitments - for almost 1,000 devices and deliveries started at the end of January 2016.

The company said it now requires a second round of funding to "ensure we can build a constant supply of product before our partners start marketing Nano".

"Our first objective is to achieve sales of 2,500 devices and reach a point where the company is self-sustaining through ongoing subscriptions and sales," it added.

The business is one of a number of British start-up firms to receive a boost from the Scot, who has two terriers, Maggie May and Rusty, and has often spoken about his love for dogs.

He has also backed Beeline and Blow Ltd, both listed on Seedrs.

He said: "Giving recognition and support to British entrepreneurs is really important to me, especially those who are the driving force behind growth-focused businesses. Every one of these entrepreneurs is passionate and dedicated to succeeding and I'm excited to have invested in their future growth."