This situation remained until 1973 and a large proportion of Sevens sold in the United Kingdom were delivered in kit form as a result.

[6] The series II had problems with its Standard Companion estate car rear axle and differential, unable to cope with the high power and cornering forces of the Seven.

[7][8] In 1970, Lotus radically changed the shape of the car to create the slightly more conventional sized Series 4 (S4), with a squarer fibreglass shell replacing most of the aluminium bodywork.

Until now, most Sevens in the UK had been sold in kit form in order to avoid paying purchase tax.

However, once the UK joined the EEC on 1 January 1973, the VAT system was adopted instead so the tax advantage of the kit-built Lotus Seven came to an end.

Accordingly, in 1973, Lotus decided to shed fully its "British tax system"-inspired kit car image.

As part of this plan, it sold the rights to the Seven to its only remaining agents Caterham Cars in England and Steel Brothers Limited in New Zealand.

[9][10] Steel Brothers had a much wider range of factory options than the UK models with carpet, centre console glove-box, radio, window-washer and hardtop.

Sold largely to competition enthusiasts, the NZ cars also had engine modifications, close-ratio gears, and adjustable suspension as factory options.

With officially licensed production stopping in 1979, the last Lotus badged Seven, a Series 4, was therefore produced in New Zealand.

[14] A car with a tuned Ford 1172 cc engine and close-ratio gearbox was tested by the British magazine The Motor in 1958.

They commented that car could be bought in component form and then it would have cost £399 for the parts from Lotus, £100 for the Ford engine and gearbox and £27 for the BMC rear axle.

[16] In addition, clamshell style wings tend to create drag and generate lift at higher speeds.

Cycle wings help alleviate this tendency, and low height Brookland aeroscreens or the lighter Perspex variants that can replace the windscreen help improve top end speed.

Nearly all Sevens, due to their extremely light weight (around 10cwt / 500 kg) have excellent acceleration, especially up to 70 mph (110 km/h), depending on power.

The original late 1950s Sevens could beat most contemporary saloon cars—and by the early 1960s, with improved Ford-Cosworth engines could take on most high-performance sports cars with 0–60 mph time in the low 7 seconds.

The front/rear weight distribution is nearly equal and the lack of a boot and small petrol tank assure that it remains fairly constant.

One disadvantage of live axles is higher unsprung weight, affecting handling and ride on rough surfaces.

It is a stressed skin construction,[citation needed] in which the flat aluminium body panels, and especially the floor, stiffen and effectively triangulate the largely rectangular steel tubular frame structure.

A front-mounted engine driving the rear wheels (a similar layout to most cars of the day) and a very lightweight steel spaceframe was covered with stressed aluminium panel bodywork.

[18] The body panels were mainly flat to avoid the expense of more elaborate curved bodywork, and the simple cloth lined plastic doors were hinged from the windscreen.

The nose-cone and wheel arches were originally aluminium parts, but these were replaced in the later S2 and S3 models with painted or self-coloured fibreglass.