There are a number of tax free options available to punters these days, most notably with online bookmakers. Many offer tax free betting or tax at a reduced rate. By shopping around on the internet you can find the best deal for yourself. For example, one firm may be charging a small amount of tax but offering a price which more than compensates for the tax burden. In this case it will be value to bet with this firm.
Some bookmakers also offer offshore, tax free telephone accounts.
The latter is much better, and I use it regularly. If you want to back a horse you can generally get a bigger price than the live show from the track, and if you want to lay a horse it's about the only way you can do it. It's also pretty good for football, although some of the more obscure markets and minority sports don't see much action. The odds offered by all three channels are Coral Eurobet prices. Just covert the fraction directly to a decimal and add 1.