False widows have been around for 150 years or more in the UK.
The press (especially the less reputable tabloids) regularly produce articles describing stories of people almost dying from their bites, losing limbs etc... However, in truth "...being bitten by a spider is very unlikely in this country in normal circumstances, and the effect of a bite is unlikely to be worse than being stung by a wasp or bee. A more serious problem is only likely to arise in the event of an allergic reaction, infection of the bite or if the person is already compromised by other health issues..."
Read the full British Arachnological Society's (the spider experts in the UK) article of this type of spider - in the link below (click the picture below).
Don't trust any pest control company that tells you they are dangerous, advising you to spend 100's perhaps 1,000's on a treatment.
There are some situations where a treatment may be needed - these are rare. We once did a treatment for example for an commercial air conditioning filter cabinet, where someone had to get into the cabinet, to re-new the filters, but the cabinet was full of false widow spiders.
Call MG Pest Control if you want to know more.