It is unpredictable whether a new tuner would be any better than your current one. It is possible that your existing tuner has developed a fault, and that a new one might be better. But it is equally possible that a new tuner would be similar to, or worse than, your existing tuner.Do you think it's worth buying another dvb tuner?
An alternative to a new tuner might be to buy an aerial amplifier. But there is no guarantee that this would result in any improvement. If the TV signal is suffering drop-outs, there won't be anything for the amplifier to amplify during the drop-outs. Aerial amplifiers can be purchased from shops such as B&Q, Homebase, and Robert Dyas.
Difficult reception tends to occur when there is a high-pressure system over the UK. This is more frequent in the summer. So you may find that TV is watchable most of the time during the winter, but only occasionally watchable during the summer.
If you cannot improve your aerial system, perhaps you need to consider using streaming services to watch TV via broadband. The major broadcasters offer "catch-up" services, and there are also the subscription services such as Netflix and Amazon Prime. For this to be practical, you need to have a broadband service that has no limits (or has very high limits). I don't use broadband TV because my contract (with BT) limits me to 15GB per month, after which I have to pay £2.20 per gigabyte. A single one-hour HD programme is about 2GB, so my entire monthly allowance would be consumed by only 8-10 hours of TV.
-- from CyberSimian in the UK