I just read that 70K puts you in the top 5% of the population. That seems loads if you live in e.g. Liverpool (my hometown) where the average house price for a 3 bed semi is around £160K. If you Iive in central London that house would be £633K. In my commuter town to London, that house price would be about £350K. So, how do you define rich? Not all of the top 5% are living in stately homes and have pads in Antigua. Most of these 70K people in the SE have a bit left over at the end of the month, but not that much after paying 50-60% of their net salary in mortgage on top of the highest council tax in the country. If they live in a commuter town they will pay around £4K a year train fares.
Taxing these people is a false economy. The only thing it does is make other people feel better that those rich bastards have got what they deserve.
Within this 5% the very, very rich will get their accountants to fudge numbers and move stuff so you can't tax it. The others will stop spending money to balance the effect of the tax rises. Usually someone who works in London works a 9-11 hour day then has at least an hours commute. To make up for the long hours they pay people to iron shirts, do their gardens and clean their pads. At best these people will drop these luxuries, curtail weekends away and holidays and stop spending money in the shops. Some will have to stop sending their DC to private school, may move to a grammar area and spend some money on tutors for maths and english. They will stop paying for DC's private dental because they can't be arsed to wait for an appointment and suck it up to save money.
At worst they will look for jobs overseas. I used to live overseas where I paid 15-17% tax with no other taxes on top. My job was to relocate expats from around the world into top jobs. The no. 1 reason why Brits left the UK (young, 30 something professional people, mainly working in finance, but also engineers, Doctors and IT) was because of taxes. They felt that they were working really long hours and had nothing left at the end of the month. Moving abroad = better quality of life and savings. In my first year I moved 250 Brits earning 100K over to one city. Some of you mentioned where are they going to go? You can add to your list HK, Singapore, Jakarta. Dubai, Abu Dhabi, KL, Australia, Bangkok where our loss is their gain and they are welcomed with open arms. Their economies have been greatly helped by our "talent".
Be careful what you wish for as it may not pan out the way we expect.