Misleading and aggressive sales tactics, colloquially called "pressure selling" are prohibited by the Consumer Protection from Unfair Trading Regulations 2008, specifically Regulation 3:
Prohibition of unfair commercial practices
3.—(1) Unfair commercial practices are prohibited.
(2) Paragraphs (3) and (4) set out the circumstances when a commercial practice is unfair.
(3) A commercial practice is unfair if—
(a)it contravenes the requirements of professional diligence; and
(b)it materially distorts or is likely to materially distort the economic behaviour of the average consumer with regard to the product.
(4) A commercial practice is unfair if—
(a)it is a misleading action under the provisions of regulation 5;
(b)it is a misleading omission under the provisions of regulation 6;
(c)it is aggressive under the provisions of regulation 7; or
(d)it is listed in Schedule 1.
[Please note: Regulations 5, 6 and 7, and Schedule 1 are quite lengthy so I have not reproduced them here to keep my answer manageable, and trust the links suffice.]
The offences may be found at Part 3, specifically Regulations 8 to 12:
8.—(1) A trader is guilty of an offence if—
(a)he knowingly or recklessly engages in a commercial practice which contravenes the requirements of professional diligence under regulation 3(3)(a); and
(b)the practice materially distorts or is likely to materially distort the economic behaviour of the average consumer with regard to the product under regulation 3(3)(b).
(2) For the purposes of paragraph (1)(a) a trader who engages in a commercial practice without regard to whether the practice contravenes the requirements of professional diligence shall be deemed recklessly to engage in the practice, whether or not the trader has reason for believing that the practice might contravene those requirements.
9. A trader is guilty of an offence if he engages in a commercial practice which is a misleading action under regulation 5 otherwise than by reason of the commercial practice satisfying the condition in regulation 5(3)(b).
10. A trader is guilty of an offence if he engages in a commercial practice which is a misleading omission under regulation 6.
11. A trader is guilty of an offence if he engages in a commercial practice which is aggressive under regulation 7.
12. A trader is guilty of an offence if he engages in a commercial practice set out in any of paragraphs 1 to 10, 12 to 27 and 29 to 31 of Schedule 1.
The penalties for these offences are at Regulation 13:
13. A person guilty of an offence under regulation 8, 9, 10, 11 or 12 shall be liable—
(a)on summary conviction, to a fine not exceeding the statutory maximum; or
(b)on conviction on indictment, to a fine or imprisonment for a term not exceeding two years or both.