I think you are being somewhat pessimistic here, Kenno Old Chap
Firstly, you can work out the rough relative worth of your cash by dividing 72 by your chosen inflation rate - if you say inflation will be a constant 5% per annum (unlikely but hey, you get to chose your own numbers) then you get 72/5= 14.4 which means your money will halve in value in 14 years. If you pick a more reasonable 3% then your money will halve in value in 24 years.
So, I intend to retire in about 20 years, which means I would need roughly twice as much money when I retire to buy the same things. As your dad has just retired I assume you are a similar age to me and will broadly need the same requirements.
Now you need to decide how much you will need to live on when you retire. But first you need to accept a few facts, that most people ignore when they look at funding a pension:
Firstly you will have paid off your mortgage. This is almost guaranteed as your mortgage lender will not just let you retire before the mortgage term is up (you are asked about this when you take a mortgage - good luck on lying about it). That is a lot of disposable income returned.
Secondly, you may want to downsize your house, you may not, but with no kids at home and no need to be in the commuter belt anymore you may find it makes sense to move house. If you do so you can get a nice big chunk of equity towards your pension.
Thirdly, you won't need the same amount of cash as you do now, you won't need two big cars, you won't do all that commuting miles and you won't need to pay all of the work related outgoings that you do now, and you won't pay the same level of income taxes as you do now - pension tax rates are quite generous and with the rise of the tax free level to £10,000 you will get a far bigger percentage of your money as take-home than you get from your salary. Obviously you won't need to pay into your pension either.
Finally, it is unreasonable to expect that you will get the same amount of money when you retire as you get when you are working - even final salary deals (if you can get one) work out your pension based on 60ths if you are lucky or more likely 80ths - realistically a final salary pension should be expected to pay about half your final salary, as a good guideline.
So, how much do you actually need? My monthly outgoings less pension and mortgage are about £600, not including food, petrol etc (I am basically talking about direct debits here), we spend about £150 a week on food and need another £300 per month for yearly car stuff like tax and insurance, and another £300 for fuel. So if we look at a base of about £1500 per month which is about £18000 per year, give or take.
And there are two of us, so that equals 9 thou a year to pay all the bills, run a car and eat stuff. Obviously if you are on your own you need to earn the money all on your ownsome, but you would need less food, a smaller house, fewer cars etc and you'd have to do your own maths.
However, £9k in today's cash would need to be £18k in 20 years time. To achieve that, and starting now, I would need to put away somewhere in the region of £600 per month to meet that, which is an amount I can justify (I already put £600 a month away and I have been paying into various pensions for the last 15 years) - I know my maths don't include any spending money, but I am assuming the reductions in current spending will make up for that, particularly the car running costs.
OK, if you are planning on working for the next 40-50 years like you say then you would need more money in the pot, but you would have more than twice as long to pay for it (and assuming you are at least mid thirties now you would be 75-85 so you would get a very good deal on your pension) and if you are much younger than that then what the hell are you doing worrying about pensions for? Buy a house for Christ's sake.